Solve for b. [sqrt] b^4/25=4

Question

I do not know how to type two of the possible answers.

Answer 1

√b^4 = b^2
√25 = 5

so, you have

√(b^4/25) = b^2/5 = 4
b^2 = 20
so, b = ±√20

Those are the only two real answers. If you want the other two answers, you have to consider that

b^2/5 = -4
b^2 = -20
b = ±√20 i