Grandpa is 6 years less than 6 times junior’s age. Let’s translate that in math form.
6 times juniors age(j) minus 6
6j - 6
The sum of their games is 78. Add Junior’s age with Grandpa’s.
6j-6 +j = 78.
Now add like terms and solve for j.
7j-6 = 78
+6 +6
7j= 84
———-
7
j= 12
Junior is 12 years old.
Substitute j to Grandpa’s equation.
6(12) - 6
72 -6
66
Grandpa is 66 years old.