How many solutions do the following equations have?
1. y = -5-x, y = x + 5
2. y = 4(1.2)x, y = x + 7
3. y = (0.5)x, y = 6

1. 1 solution see graph 1 (-5,0)
2. 1 solution see graph 2 (1.842,8.842)
3. 1 solution see graph 3 (12,6)

These are all straight lines so they are only going to intersect once.  Unless you have something like a square or cube where you get a curve in the line, it will always only have one solution.

Hope that helps.