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
