1. **State the problem:** We are given a Cobb-Douglas production function with productivity of resources $A=12$, capital $K=36$, and labor $L=4$. We need to find the total productivity of labor. 2. **Recall the Cobb-Douglas production function:** $$Y = A K^\alpha L^\beta$$ where $Y$ is total output, $A$ is total factor productivity, $K$ is capital input, $L$ is labor input, and $\alpha$, $\beta$ are output elasticities of capital and labor respectively. 3. **Assumptions:** Since $\alpha$ and $\beta$ are not given, we assume constant returns to scale with $\alpha + \beta = 1$. For simplicity, assume $\alpha = 0.5$ and $\beta = 0.5$. 4. **Calculate total output $Y$:** $$Y = 12 \times 36^{0.5} \times 4^{0.5}$$ Calculate each term: $$36^{0.5} = 6$$ $$4^{0.5} = 2$$ So, $$Y = 12 \times 6 \times 2 = 144$$ 5. **Calculate total productivity of labor (TPL):** TPL is output per unit of labor: $$TPL = \frac{Y}{L} = \frac{144}{4} = 36$$ **Final answer:** The total productivity of labor is $36$ units.