First of all we group our m's together.
So first add
5m + 4m = 9m
Now lets set up our equation again
9m = 72 .... divide both sides by 9 to get m alone
÷9 = ÷9
************ now m is alone on the left side and we solve on the right side.
m = 8
So your answer is
m = 8
I didn't learn this. Sorry
These are my notes on different types of angles, including alternate angles!