Easy peasy
the midpoint between

and

is

just average them
so given that (3,5) is the midpoint of (-4,5) and (x,y)

so by logic

and

times both sides by 2 for everybody
-4+x=6 and 5+y=10
add 4 to both sides for left one and minus 5 from both sides for right
x=10 and y=5
the coordinate of point C is (10,5)
the x coordinate is 10
5*3+2=17 it's A, 3 in this equation.