Algebra please answer

Question

What’s the answer? Suppose P varies jointly with r and the square of e. When r=6 and e=6, then P=648. Find P if r=7 and e=3

Answer 1

P = kre^2 = 648 = k(6)(6^2

k = 648/6(36) = 3

P = 3re^2

when r = 7, e=3

P = 3(7)3^2= 189