Answer :
It is answer choice D.
7.50 + p = 9.50
-7.50 -7.50
the 7.50 and 7.50 cancel out and you are left with p=2.50
7.50 + p = 9.50
-7.50 -7.50
the 7.50 and 7.50 cancel out and you are left with p=2.50
D: because if you take 9.50-7.50=2 you would get p=price or the price of the pen.
Hope I helped=)
Hope I helped=)