If the supply curve of labour market is given as S = 4L + 8. What is L when s = 20?

Analyze the question You are given a labour supply function, S = 4L + 8, and asked to find the quantity of labour (L) when S = 20.

Concept A supply function shows the relationship between the quantity supplied and its determinants. Here, S is expressed in terms of L. To find L, substitute the given value of S and solve the resulting linear equation.

Step-by-step solution

1. Write the equation: S = 4L + 8

2. Substitute S = 20: 20 = 4L + 8

3. Subtract 8 from both sides: 20 − 8 = 4L 12 = 4L

4. Divide both sides by 4: L = 12 ÷ 4 = 3

Check: 4(3) + 8 = 12 + 8 = 20 ✓

Answer: L = 3, which is option D.

Tip: For "find the variable" questions with a linear equation, do two things: isolate the term with the unknown (subtract the constant) and then divide by its coefficient. You can also test each option quickly by plugging it back in. Only L = 3 gives S = 20 here, since the others give 16 (L=2), 24 (L=4) and 28 (L=5).