Find the other endpoint of a line segment with the given midpoint and one endpoint

Question

Endpoint: ( 6, -1); Midpoint: 15/2, 2

A. 9,5 B. 2,15/2 C. -3, -6 D. 15, 4

Answer 1

(x+6)/2=15/2
x + 6 = 15
x = 9
(y - 1)/2 = 2
y - 1 = 4
y = 5
so I get (9,5)