Solve the simultaneous equations: (a) y - 2x = 6; (b) y+2x = 0.

rearrange equation (a) to be: y = 6 + 2x. Substitute this into equation (b) to get: (6 + 2x) + 2x = 0

rearrange this to get: 6 + 4x = 0. Simplify to get x = -(6/4). Get the value for x to be: x = -1.5.

substitute this x value into equation (b) to get the value for y, hence we get: y + 2(-1.5) = 0; y = 3.