Slope intercept form is y = mx + b, where m is the gradient or slope and b is the y-intercept.
To find the gradient/slope (m), we need to do change in y ÷ change in x.
Pick two co-ordinates on the line; (0, 5) and (-2, 0)
Subtract the y co-ordinates; 5 - 0 = 5
Subtract the x-co-ordinates; 0 - -2 = 2
Finally, divide 5 by 2; 5 ÷ 2 = 5/2 or 2.5
Now we have y = 2.5x + b. The y-intercept is simply where the line crosses the y axis (it crosses at 0,5). This means the equation of the line is y = 2.5x + 5.