If the commutative property indicates that a+b=b+a with the problem being 98,551+2,841=2,841+n, its a pretty safe assumption that n would equal 98,551. a would be 98,551 as b would be 2,841.
Let’s represent his sister’s sales as x
3/4ths of his sister’s sales would be:
3/4x
3 less than 3/4ths of his sister’s sales would be:
3/4x - 3