If $(x + 2)(3x^2 - x + 5) = Ax^3 + Bx^2 + Cx + D$, what is the value of $A + B + C + D$?
I need to find the coefficients of the cubic polynomial on the right-hand side of the equation. To do that, I can multiply out the left-hand side using the distributive property. I get $(x + 2)(3x^2 - x + 5) = 3x^3 + 6x^2 - x^2 - 2x + 5x + 10$. Simplifying, I get $3x^3 + 5x^2 + 3x + 10$. Comparing this with the right-hand side, I can see that $A = 3$, $B = 5$, $C = 3$, and $D = 10$. Adding these up, I get $A + B + C + D = 3 + 5 + 3 + 10 = 21$. 