"+-" should always be changed to "-".
You have 3 - 7 - 2. You may evaluate this from left to right, obtaining -4 -2, or -6.
4 - 16 -2(2) involves multiplication, which must be carried out before addition or subtraction. Thus, 4 - 16 - 4. Working from left to right, we get -12 - 4 = -16
