The distance formula of an equation would be the square root of x2 - x1 + y2 - y1 however you have the same y values meaning you find the distance by subtracting the xs!
it is 12... 20-8 = 12... u do that cuz the slope of the two points is 0.. so it is a horizontal line and you don't have to use the formula.... u just subtract the x values.