1. **State the problem:** We are given the supply function $Q = 200 + 0.75P$ and asked to find the autonomous supply. 2. **Understand the concept:** Autonomous supply is the quantity supplied when the price $P$ is zero. It represents the intercept of the supply function on the quantity axis. 3. **Apply the formula:** To find autonomous supply, set $P = 0$ in the supply function: $$Q = 200 + 0.75 \times 0$$ 4. **Calculate:** $$Q = 200 + 0 = 200$$ 5. **Interpretation:** The autonomous supply is 200 units, meaning even if the price is zero, the supplier is willing to supply 200 units. **Final answer:** $$\boxed{200}$$