Let us assume that the number of quarters Greg has = x
Then the number of quarters Don has = 2x +3
Together they have 18 quarters
then
x + 2x + 3 = 18
3x = 18 - 3
= 15
x = 5
So the number of quarters Greg has is 5
Then the number of quarters Don has = 2x + 3
= (2 * 5) + 3
= 10 + 3
= 13
So it can be concluded that Don has 13 quarters.