Grandmother is 3 years younger than grandfather. Nine years ago, the sum of their ages was 105. How old are they?

Answer 1

Now:
grandpa --- x
grandma --- x-3

nine years ago:
grandpa ---- x-9
grandma ---- x-3 - 9 = x - 12

translate "Nine years ago, the sum of their ages was 105" into math
x-9 + x-12 = 105

carry on ....

Answer 2

X-9+x-12=105
X+x=105+9+12
2x=126
X=63

Grandmother x-3
63-3=60

Grandfather x
63