let's say, the total sales is "x"... .so hmm on Plan A, he gets 350 plus 7% of "x", well, 7% is just (7/100) * x or 0.07x
now, on Plan B, he gets 436 plus 5% of "x", 5% of "x" is (5/100) * x, or 0.05x
he's better off with A, only if A is greater than B, namely,
A > B
and surely you know how much that is.