First, distribute -3 to everything in the parentheses: -3(5 + -1d) = -15 + 3d. You are left with -15 + 3d = 2d + 10. Next, move like terms to the same side of the equation. You are left with d = 25. Substitute d = 25 to double check the answer. -3(5 + -1(25))...