If the graph of the line y = ax + b passes through the points (4,5) and (8,11)$, what is a - b?
a is the slope and b the y intercept. We solve for the slope first. Plugging the points into the slope formula, we find that a is 6/4=3/2. So now we have y=3/2x+b. Then we plug in either of the given points to solve for b.
Therefore the equation of the line is y=3/2x-1.