To find the answer, simply substitute each choice into the equation.
6-3>4
3>4
The answer is not 6 as 3 is less than 4, not greater than it.
7-3>4
4>4
The answer is not 7 as 4 is not greater or less than 4, it is equal to 4.
8-3>4
5>4
The answer IS 8, as 5 is greater than 4.