Hi hi help me please please

22.5 cm

Step-by-step explanation:

Step 1: Identify the similar sides ( from ABC and FGH )

ABC to FGH ; ABC to FGH ; ABC to FGH

AB is similar to FG

BC is similar to GH

AC is similar to FH

Step 2: Find ratio between two triangles:

Because sides AB and FG are similar, we want to find the ratio between them so we can find the unknown side.

AB = 6 ; FG = 15  15/6 = 2.5

This ratio is consistent with BC to GH ( 12.5/5 = 2.5 too )  

Step 3: Use ratio to find unknown side:

The side similar to our unknown side is AC ( from the fact that ABC to FGH ),

So if we multiply AC by the ratio, 2.5, we get our unknown side of 22.5