The answer is True because JKL and PNM are proportional. If they are proportional, JK is proportional to PN, NM is proportional to NM and JL is proportional to PM.
All you need to do is find (f+g)x = (12x) + (10(1.2)X) which = 24x then in the multiple choice, see which one equals 24x, in this case its C. 5*1.2=6, 6x+6x = 12x*2 = 24x