1. **State the problem:** Jessica baked 72 cookies and sold $x$ cookies. Max baked 36 cookies and sold half as many cookies as Jessica, so Max sold $\frac{x}{2}$ cookies. 2. **Set up the equation:** Both had the same number of cookies left over. Jessica's leftover cookies are $72 - x$. Max's leftover cookies are $36 - \frac{x}{2}$. Since leftovers are equal: $$72 - x = 36 - \frac{x}{2}$$ 3. **Solve the equation:** Multiply both sides by 2 to clear the fraction: $$2(72 - x) = 2\left(36 - \frac{x}{2}\right)$$ $$144 - 2x = 72 - x$$ 4. **Isolate $x$:** Add $2x$ to both sides: $$144 = 72 - x + 2x$$ $$144 = 72 + x$$ Subtract 72 from both sides: $$144 - 72 = x$$ $$72 = x$$ 5. **Interpret the result:** Jessica sold 72 cookies. 6. **Check the options:** The answer is D. 72.