A^2 = B^3*C^4 ==> B^3 = (A/C^2)^2 ==> B = (A/C^2)^(2/3) ==>

B' = (2/3)[(A/C^2)^(-1/3)](A'C^2 - 2ACC')/C^4 ==>

B'(7)=(2/3)[(A(7)/C^2(7))^(-1/3)](A'(7)C^2(7) - 2A(7)C(7)C'(7))/C^4(7)

IWe know what C(7) and A'(7) is, so we only need A(7) and then substitute:

A^2(7) = B^3(7)*C^4(7) = (3^3)(2^4) = 27*16 = 432

Tonio