Answer: 15
<u>Step-by-step explanation:</u>
small: 5 12 13
middle: __ 36 39
large: 45 108 117
Notice that to get from the small to the large, multiplied by 9
5(9) = 45 12(9) = 108 13(9) = 117
That is because the sides are proportional
To get from small to middle, multiply by 3
5(3) = 15 12(3) = 36 13(3) = 39
To solve it using proportions: