12 + 4 · 3 - 15
To solve this, we have to use the order of operations. In the order of operations, multiplying and dividing come first while addition and subtraction come later.
12 + 4 · 3 - 15
= 12 + 12 - 15
The order doesn't matter for subtraction and addition, since you'll end up with the same answer. (In this case, I'll be doing addition first to avoid negative numbers)
12 + 12 - 15
= 24 - 15
= 9
That's your answer! Happy Studying~