Concept:The supply equation relates the quantity supplied S to the quantity of labour L.Explanation:Given the supply function: S=4L+8.Substitute the given value S=20 into the equation.So, 20=4L+8.Subtract 8 from both sides: 20−8=4L.This gives 12=4L.Divide both sides by 4: L=412.Therefore, L=3.Answer:L=3Option D.