If you can see if you can on some of my

PQ // BC 

then

Angle P = Angle B, A is common angle the two triangles are similar

AP/AB  = AQ/AC

8/18 = 12/ AC

AC = 12 * 18/8 = 27 (your ans: D)

AQ + QC = AC

QC = AC - AQ = 27 - 12 = 15 (if it was required) 

tan60 = y/8

y = s tan60 = 8sqrt(3)  (B)

Next time, post each question separately.