The two points (0,0) and (4,5) are on the line. The points are marked in blue in the attached image below.
Use the slope formula to get
m = (y2-y1)/(x2-x1)
m = (5-0)/(4-0)
m = 5/4 <----- this is the answer in fraction form
m = 1.25 <----- this is the answer in decimal form
The idea of the slope formula is we're subtracting the y values together, then subtracting the x values together in the same order, finally we divide the two results and reduce if possible to get the fraction form. Use long division or a calculator to find the decimal form of the fraction. In this case, the rise is 5 and the run is 4. Meaning we go up 5 units and over to the left 4 units to go from (0,0) to (4,5).