The correct option is C 15
Because the triangles are similar, corresponding angles are congruent and corresponding sides are proportional.
First find the scale factor:
Since AC=12 and PR=18, the scale factor is found by dividing PR by AC
Scale factor = 1812 =1.5
(That means that the second triangle is 1.5 times as large as the first)
Now use the same scale factor to find the length of QR:
QR=1.5×10=15