R varies jointly as r and B^2. When r=3, and B=3 R=135. Find R when r is 1

Question

and B=10.

Answer 1

R = krB^2
135 = k(3)(3^2) = 27k
k = 5

So, R(r,B) = 5rB^2
R(1,10) = 5(1)(100) = 500