So here the 'unit rate of change' means the slope. It's also referred to as 'rise over run'. A line can be expressed in the form y=mx+b, where m is the slope and b is the y intercept. So here, m is equal to 0.4 and the line is y=0.4x
Think of it this way: if you plug in 1 for x, you get 0.4 for y. So that matches what the problem was saying about a change of 1 unit in x means 0.4 units in y. To graph it, start at 0,0 and move 0.4 up in y direction (rise) and 1 to the right in the x direction (run). If you keep doing that and connect the points, that will be the line
