4. The fruit trees are planted so that there are 15 fruit trees in each row. If there were 6 fewer rows in the orchard, but 5 more fruit trees in each row, then there would be a total of 10 more fruit trees in the entire orchard. How many rows of fruit trees are planted?
4. Let $x$ be the number of rows of fruit trees in the orchard. Then there are $15 \cdot x$ fruit trees in the orchard.

$1 \text{ POINT}$

If there were 6 fewer rows, and 5 more fruit trees in each row, there would be

$20 \cdot (x-6) = 20 \cdot x - 120 = 15 \cdot x + (5 \cdot x - 120)$ fruit trees in the orchard.

3 POINTS

Thus, the number of fruit trees differs by $5 \cdot x - 120$, and according to the condition of the problem, this difference is equal to 10.

So, $5 \cdot x - 120 = 10$, hence $5 \cdot x = 130$, from which $x = 130 : 5 = 26$.

Therefore, 26 rows of fruit trees have been planted.