The diagram is a mess of lines; you have to guess where that 12 belongs. Just to make the question a bit more interesting, I'm going to say the 12 belongs to the perpendicular.
If that's true you can find KT using Pythagorus. KT and RT are equal. (SSS)
So, let's go.
Givens
1/2 of ST = 1/2 32 = 16
12 is the leg of the small triangle KT and the third point where the perpenduclar line meets ST.
Solution
KT^2 = 16^2 + 12^2
KT^2 = 256 + 144
KT^2 = 400
KT = sqrt(400)
KT = 20
RK = KT because parts of a congruent triangle = parts of the other triangle containing the line (KT) that you are trying to find the length of.
