The missing measure is 26.13............
I believe the answer would be 6:5 because you divide both 18 and 15 by 3.
You need to use the order of operations to solve this, which is PEDMAS; however, there is no real order of if division should come before multiplication or vice versa, so you do it in the order it appears in the problem. This is true for addition and subtraction as well.
-8 / -2 = 4
4 • 6 = 24
5+24 = 29
Your answer is 29
