This is a binomial subtraction problem.
It can be written as:
(6x-7)-(2x+3)
Binomial subtraction problems require one to phrase the problem as addition by flipping the signs.
(6x-7)+(-2x-3)
Now we can simplify:
6x-7-2x-3
4x-7-3
4x-10
So the answer is 4x-10 more pairs of shoes than China.
