In the xy-coordinate system, if (m, n) and (m + 5, n + k) are two points on the line with the equation x = 2y + 5, then k =  Choose the correct choice from the following answers:
A) 1 / 2	B) 1	C) 2	D) 5 / 2	E) 4

Rationale: "since ( m , n ) and ( m + 2 , n + k ) are two points on the line with the equation x = 2 y + 5 they should satisfy m = 2 n + 5 and m + 5 = 2 * ( n + k ) + 5 . by 1 st equation we have m - 2 n = 5 and by 2 nd equation m - 2 n = 2 k - - - > 5 = 2 k - - - > k = 5 / 2 . the answer is , therefore , ( d ) ."
Answer: D