Answer: 30
Step-by-step explanation: Assuming that the side lengths correspond with one another you can set up a ratio to solve
It should look something like this: 15/25 = 18/x
With this equation set up you can solve by cross multiplying. 25(18)=15x
Then start sloving:
25(18)=15x
450=15x
450/15=15x/15 (divide both sides by 15)
30=x