From (-4,-9) to (1,1), Δx = 5 and Δy = 10. If we divide the line into 5 equal pieces, each piece is increased by Δx = 1 and Δy = 2 from the previous point. After 3 pieces, the coordinates are (-4+3,-9+6) which is 3/5 of the total length with 2/5 remaining.
