Help I keep getting the wrong answer

Seven years ago, Grogg's dad was 6 times as old as Grogg, and 4 years ago, his dad was 4 times as old as Grogg. How old is Grogg's dad currently?

Think about these two equations and what they mean:

(D is Dad & G is Grogg)

D - 7 = 6(G - 7)

D - 4 = 4(G - 4)