Question

An oak tree is 6 times as old as a pine tree and an elm tree is 6 years younger than the oak tree. In 3 years, the age of the elm will be 3 times the age of the pine. How old is the oak tree now?

Answer 1

oak = x; pine = y; z = elm
equations (in order of the sentences) are:
6x = y
z- 6 = x
3z = y +3

Answer 2

So i would use sustitution :)