
If a line is drawn through (twenty, seventy) and (twenty-five, sixty), then you can use the points in getting the equation.
Slope is = (60-70)/(25-20) = -2
Using the two-point slope form, y – y1 = m(x – x1)
               y – 70 = -2(x – 20)
               y – 70 = -2x + 40
               y = -2x + 110