DS Geometry question - GmatPrep Question

[falu09]

I have attached a screen shot of the question. Please help explain answer. I will post Official Answer after explanations!

Thanks!

[provemba]

Let angle PQR be x, QPR be y and PRS be z.
Therefore angle QRP = 180 - z
in traingle PQR, sum of the angles is 180 = x + y + 180 - z
z -x = y
Question asks to find z -x

by condition 1
y = 30. Hence z - x = y = 30

by condition 2
x + 180 - z = 150
z - x = 30
Hence D

[falu09]

Thanks for the explanation! I was trying to figure out the degree's of all angles instead of thinking like you and just seeing that all i needed was to figure out what z - x was!