The equation you are looking for is (a ÷ 4) - 6.
The quotient is the answer you get from a division problem. With that being said, since you are subtracting 6 from the quotient, you must put a ÷ 4 in parenthesis, and follow the parenthesis with "- 6".
Thus meaning the equation is (a ÷ 4) - 6. I hope this helps!