First of all, let's find the slope, which is the rise/run. We have the points (-4,-3) and (-2,0). To get the run there, we move to the left two units. We rise up three units as well. Therefore our slope is positive. We have rise/run, which is 3/2 as our slope.
Now, b is the y-intercept, or when our line intersects with the y-axis. We can see that it intersects at a y-value of 3.