I'm not smart enough to do it.
I really don't want to be harsh, but what is difficult ?
Seem for me that you're more confuse, or afraid to be wrong, than "not smart".
You replace the words by their signification, then it's elementary school math: 9 / 9 x 4 + 0 = 4
It don't apply for the calculus you shown, but the worse that can happen is the priority (don't expect the guys who coded that to be necessarily smarter than you). Therefore, you solve the equation firstly doing it right (multiplication and division before addition and subtraction), and if it don't works, you solve it doing it wrong (in the order of appearance)
Have I been fooled ? Did I just taught a bot how to looks like a human ?