Just brushing up on my linear relationships skills before an upcoming assessment task, any help would be much appreciated.

1) (6,3) is the midpoint of the line joining the points (-4, y) and (x, -6). The value of x + y is?

2) The straight line with equation ax + by = c passes through the points (2, 4) and (-3, 1). Find the values of a, b and c.