The formula for measuring elasticity is percentage change in quantity supplied/percentage change in price
The midpoint approach would take the difference in quantity (Q2-Q1) and divide that by the average of the quantities (Q2+Q1)/2. And then the same for price.
Then would would divide both of those to get the coefficient.
So quantity: 1,400-1,200 / (1400+1200)/2= 200/1300 = .154
Then price: 24-20/ (24+20)/2 = 4/22 = .182
Then divide: .154/.182 = .85 this is your coefficient
C. Being that the coefficient is less than 1, we would say that the supply is relatively inelastic.