Well, you can see that WK is congruent (is that the right word?) to RN.
They even gave the measurements.
KT would be congruent to PR.
Make a ratio:
WK : RN = KT : PR
Now put in the measurements, with x as PR
14 : 24.5 = 18 : x
This will equal to 14x = 24.5 * 18.
14x = 441
x = 441/14
x = 31.5441/14 = 31.5
x = 31.5
So PR is 31.5 in.