In Exercises, four solutions of the equation y = ax3 + bx2 + cx + d are given. Use a system of four equations in four variables to find the constants a, b, c, and d and write the equation.
a. (-2, 59), (-1, 13), (1, -1), and (2, -17)
b. (-2, -39), (-1, -12), (1, -6), and (3, 16)