Well this is a good question. We can take out Y, and X because that is a variable and it isn't defined. Now what we need to figure out is B or the Y - Intercept. Something thats in every Slope - Intercept form type equation:
Y = MX + B
The Y - Intercept is basically the y value when x is 0. A handy tip is that whatever value of y that is on the vertical line in the graph is B. If we look at the graph for Question 6 we find that it is +9. Since Y = X + 9 is the only equation that has +9 as it's B or Y - Intercept we can figure out the first one.
Using our handy tip from above, let's do the same for 7. This time the line intercepts the vertical line in the negative value of -2. So we find that B for this equation is -2. Therefor the only equation with -2 as it's be is Y = X - 2. So that is our answer.
