You can use calculus ( related rates). Given the rate os change of the radius for example you can find the rate of change of volume using differential calculus.
Sharon's age= 2x
Brian's age= x
(2x-5)+(x-5)= 25
3x-10=25
3x=15
x=5
Brian is 5 years old and Sharon is 10
Take online tests on what you think you need work on
And also study
Sixty-nine thousand, a hundred and eight?
