easy peasy
the midpoint between [tex](x_1,y_1)[/tex] and [tex](x_2,y_2)[/tex] is
[tex](\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})[/tex]
just average them
so given that (3,5) is the midpoint of (-4,5) and (x,y)
[tex](\frac{-4+x}{2},\frac{5+y}{2})=(3,5)[/tex]
so by logic
[tex]\frac{-4+x}{2}=3[/tex] and [tex]\frac{5+y}{2}=5[/tex]
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
