This is a college textbook, and that explains how to solve it
It's a college refresher course on high school Maths. They also forgot to cover The Distributive Law, which is not unusual given college Professors don't actually teach high school Maths.
Another example
From the same refresher course 🙄
Alternatively, here is another example
Which also doesn't cover The Distributive Law, which isn't surprising given that chapter isn't even about order of operations! 😂
In case you can’t find the correct part
Still not about a(b+c). You lot are investing so much effort into such an obvious False Equivalence argument it's hilarious! 😂