cara mencari Qs jika p1 10 p2 20 dan Q1 60 Q2 80

Fungsi Qs = a + b Ps
hitungannya
P-P1/ P2- P1 = Q-Q1/ Q2- Q1
P-10/20- 10 = Q - 60/80 - 60
P- 10/ 10 = Q- 60/20
20p - 200 = 10Q -600
20P -200+ 600 = 10Q
20P + 400 = 10Q
--------------------------: 10
2P + 40 = Q
jadi fungsi Qs = 2P + 40