Halp! Linear equation questions.

I'm supposed to find the y-intercept, slope, and equation for a couple problems. I'm having a lot of trouble with these. This first one has the two points on a graph (0,3) and (6,6) The y intercept is 3 and the slope is 3, but how do I find the equation? The second one has the points (2,18) and (6,6). the slope is -3 (right?) but how do you find the y-intercept when the x-axis skips 0? How do you find the equation for that? The third one has no y intercept because X stays the same. The points are (6,3) and (6,10). There is no slope and no y-intercept, so how do I say y goes up by 7 in an equation?

Thank you SO much.(Bow)