Answer is 25
To find this you need to find the dilation ratio of one figure side to the other
Take the like sides of 5 and 12-1/2 compared to sides 10 and x
5 10
_ ____
12-1/2. X
Your dilation (make bigger) ratio from 5 to 10 is 2
So you do the same ratio to 12-1/2
Which gives you the answer of 25
I hope this helps!