Answer:
You can use the midpoint formula.
Method:
MAB = (Ax+Bx)/2 ; (Ay+By)/2
Substitute in what you have:
(2;4) = (Ax+3)/2 ; (Ay+7)/2
Because we know the x coordinate of the midpoint, we can assume that:
2 = (Ax+3)/2
And now solve for Ax:
4 = Ax+3
Ax = 1
Because we know the y coordinate of the midpoint, we can assume that:
4 = (Ay+7)/2
And now solve for Ay:
8 = Ay+7
Ay = 1
Therefore A(1;1)