A father is 4 times as old as his daughter. In 6 years, he will be 3 times as old as she is. How old is the daughter now?

F is father's age

D is daughter's age

F = 4D eq. 1

F + 6 = 3(D + 6) eq. 2

let's substitute eq. 1 into eq. 2

4D + 6 = 3(D + 6)

4D + 6 = 3D + 18

4D - 3D = 18 - 6

**D = 12**