Answer: B. x - 5 = 13
Explanation:
Since Pedro bought the picture frames for his mother, we will see what she does with them. 5 go to her sister and 13 are kept for herself. Let x be the number of picture frames Pedro buys.
5 + 13 = x
This is not one of the answer choice, but x - 5 = 13 is. If we subtract 5 from both sides of the equation we created above, this proves to be our answer.
B. x - 5 = 13