coordinates and midpoint?

Question

the midpoint of AB is (4, -3) and A is located at (1, -5). if (x,y)are the coordinates of B, what is the value of x+y

Answer 1

mid point = ( ( 1+x)/2, (-3 + y)/2 ) = ( 4, -3)
so 1+x = 8 and -3 + y = -6
so x = 7 and y = -3
therefore x+ y = 4

Answer 2

Since you know the midpoint and one of the end points this is easy.

Calculate the offsets in x and y to get from A to the midpoint:
dx = 4 - 1 = 3
dy = -3 -(-5) = 2

So the separation of the midpoint from A is 3 in x and 2 in y. To find B just add these to the coordinates of the midpoint.

x = 4 + 3 = 7
y = -3 + 2 = -1

So B is at (7,-1)
And the value of x + y is 7 + (-1) = 6