Answer: 13.5
Step by step:
1: the symbol “~” means that the two shapes are congruent in size so you know you have to multiply each side by the same number i.e: multiply all sides by the same number
2: start by taking each side and multiplying them start with the smaller shape to the largest shape
3: i multiplied 5 to get 7.5 and 6 to get 9
4 then take the 9 and multiply it by 1.5 to get your answer
Hope this helps! :)