In general,

Set up a system of equations and solve for y in terms of x.

For parts (c), (d), and (e), follow the steps in part (b).

Solving for x in the top equation and y in the bottom equation:

By substitution:

x(k + 4)(k − 7) = −30x

Since we have assumed x ≠ 0, divide by x and solve for k.