Question 407605
Since the diagonals of a parallelogram bisect each other, then we can use the midpoint formula in reverse.  For the vertex opposite (-6,4), we get:

{{{1 = (x+(-6))/2}}} ==> 2 = x - 6 ==> x = 8,
{{{1 = (y+4)/2}}} ==> 2 = y + 4 ==> y = -2.
Therefore the vertex opposite (-6,4) is (8, -2).

For the vertex opposite (-3,-1), we get:

{{{1 = (x+(-3))/2}}} ==> 2 = x - 3 ==> x = 5,
{{{1 = (y+(-1))/2}}} ==> 2 = y - 1 ==> y = 3.
Therefore the vertex opposite (-3,-1) is (5,3).