A right triangle has integer side lengths, and the sum of its area and the length of one of its legs equals $75$. Find the side lengths of the triangle.
Given a right triangle with integer side lengths, we need to find the side lengths such that the sum of its area and the length of one of its legs equals $75$.

1. Let the legs of the right triangle be $a$ and $b$, and the hypotenuse be $c$. The area of the triangle is given by:
   \[
   \text{Area} = \frac{1}{2}ab
   \]

2. According to the problem, the sum of the area and the length of one of its legs equals $75$. Without loss of generality, assume the leg is $a$. Therefore, we have:
   \[
   \frac{1}{2}ab + a = 75
   \]

3. Simplify the equation:
   \[
   \frac{1}{2}ab + a = 75 \implies \frac{1}{2}a(b + 2) = 75 \implies a(b + 2) = 150
   \]

4. We need to find pairs of integers $(a, b)$ such that $a(b + 2) = 150$. The divisors of $150$ are $1, 2, 3, 5, 6, 10, 15, 25, 30, 50, 75, 150$. We will test these values to find valid pairs $(a, b)$.

5. For each divisor $a$, calculate $b$:
   \[
   b = \frac{150}{a} - 2
   \]

6. Check if $\sqrt{a^2 + b^2}$ is an integer (i.e., $c$ is an integer).

   - For $a = 1$: $b = \frac{150}{1} - 2 = 148$; $\sqrt{1^2 + 148^2} = \sqrt{21905}$ (not an integer)
   - For $a = 2$: $b = \frac{150}{2} - 2 = 73$; $\sqrt{2^2 + 73^2} = \sqrt{5333}$ (not an integer)
   - For $a = 3$: $b = \frac{150}{3} - 2 = 48$; $\sqrt{3^2 + 48^2} = \sqrt{2307}$ (not an integer)
   - For $a = 5$: $b = \frac{150}{5} - 2 = 28$; $\sqrt{5^2 + 28^2} = \sqrt{809}$ (not an integer)
   - For $a = 6$: $b = \frac{150}{6} - 2 = 23$; $\sqrt{6^2 + 23^2} = \sqrt{625}$ (integer, $c = 25$)
   - For $a = 10$: $b = \frac{150}{10} - 2 = 13$; $\sqrt{10^2 + 13^2} = \sqrt{269}$ (not an integer)
   - For $a = 15$: $b = \frac{150}{15} - 2 = 8$; $\sqrt{15^2 + 8^2} = \sqrt{289}$ (integer, $c = 17$)
   - For $a = 25$: $b = \frac{150}{25} - 2 = 4$; $\sqrt{25^2 + 4^2} = \sqrt{641}$ (not an integer)
   - For $a = 30$: $b = \frac{150}{30} - 2 = 3$; $\sqrt{30^2 + 3^2} = \sqrt{909}$ (not an integer)
   - For $a = 50$: $b = \frac{150}{50} - 2 = 1$; $\sqrt{50^2 + 1^2} = \sqrt{2501}$ (not an integer)
   - For $a = 75$: $b = \frac{150}{75} - 2 = 0$; $\sqrt{75^2 + 0^2} = 75$ (integer, $c = 75$)
   - For $a = 150$: $b = \frac{150}{150} - 2 = -1$ (not valid as $b$ must be non-negative)

7. The valid pairs $(a, b)$ are $(6, 23)$ and $(15, 8)$. The corresponding hypotenuses are $25$ and $17$, respectively. Additionally, $(75, 0)$ is a degenerate triangle (not a valid right triangle).

Conclusion:
The side lengths of the right triangle are $(6, 23, 25)$ and $(15, 8, 17)$.

The final answer is $\boxed{(6, 23, 25)}$ and $\boxed{(15, 8, 17)}$