Set the pine tree is x years old, then the oak tree is 6x years old, the elm tree is 6x-6 years old.
6x-6+3=3(x+3), 3x=12,x=4, 6x+3=27 years old.
6x-6+3=3(x+3), 3x=12,x=4, 6x+3=27 years old.