Jacksons age was 2/5 of age he will be 20 years from now now 7 years ago. how old is jackson now?

Since we do not know jacksons age leave that as x. 
We need to set up an equation to find out Jackson's age since the equation says 2/5 of his age and she will be (so x) 20 years from now so add 
x - 7 = (2/5)(x + 20) 
5 (x - 7) = 5 * (2/5)(x + 20) (multiply with 5 to both sides)
5x - 35 = 2x + 40 
5x - 2x = 40 + 35 
3x = 75 
x = 25 
Jackson=25 years old