You can find the slope-intercept equation of a line by plugging the slope and one coordinate pair into the point-slope form, y - y_1 = m (x - x_1). M will be slope and y_1 and x_1 will be the coordinate pair.
y - y_1 = m (x - x_1) Plug in the values
y - 5 = 4/5 (x - (-15) Cancel out the double negative
y - 5 = 4/5 (x + 15) Use the Distributive Property
y - 5 = 4/5x + 60/5 Simplify the fraction
y - 5 = 4/5x + 12 Add 5 to both sides
y = 4/5x + 17