25 in exponential form: 
Factors to make 25 in exponential form: 5 * 5 = 5^2, 1 * 25 = 25^1
The answer is 59049 hope this helps
V = 4/3 * pi * r^3
V = 4/3 * 3.14 * 21^3
Simplify exponent:
V = 4/3 * 3.14 * 9261
Multiply:
V = 38772.72
Well you can solve two step equations by multiplying or adding or subtracting or dividing by the number and put a n on the answer because there is only one n in equatioN see the solve the modle