math

Here: https://web2.0calc.com/questions/john-is-3-4-the-age-of-james-three-years-ago-john

Second half of your question should read "Three years ago, John was 5/7 (NOT 5/2) the age of James".

James's age today =J 

John's age today   =0.75J

[0.75J - 3] / [J - 3] = 5/7, solve for J

[0.75J - 3] =5/7J - 15/7

[0.75J - 5/7J = 3 - 15/7

[J / 28 ] = 6 / 7

J =[6 * 28] / 7

J = 24 years - James's age today.

Actually it is supposed to read 5/2 not 5/7