Since interest is compounded quarterly, the quarterly interest rate is 0.075/4 = 0.01875.
Each time interest is credited to a current amount x, the interest is 0.01875 times x, so the new balance with interest is x + 0.01875x, or 1.01875 times x. The 1.01875 is the "growth factor" -- how much the current amount gets multiplied by each time interest is applied.
If the interest is compounded quarterly for 4 years, that growth factor gets applied to the beginning balance 4*4=16 times.
So the balance at the end of 4 years in your problem is