1. **State the problem:** We need to find how many adult tickets were sold given that child tickets cost 5.50, adult tickets cost 9.30, a total of 121 tickets were sold, and the total revenue was 870.70. 2. **Define variables:** Let $x$ be the number of adult tickets sold. 3. **Express the number of child tickets:** Since total tickets are 121, child tickets = $121 - x$. 4. **Write the total value equation:** Total revenue = (price of adult tickets) \times (number of adult tickets) + (price of child tickets) \times (number of child tickets). $$9.30x + 5.50(121 - x) = 870.70$$ 5. **Simplify the equation:** $$9.30x + 5.50 \times 121 - 5.50x = 870.70$$ $$9.30x + 665.50 - 5.50x = 870.70$$ 6. **Combine like terms:** $$(9.30x - 5.50x) + 665.50 = 870.70$$ $$3.80x + 665.50 = 870.70$$ 7. **Isolate $x$:** $$3.80x = 870.70 - 665.50$$ $$3.80x = 205.20$$ 8. **Solve for $x$:** $$x = \frac{205.20}{3.80} = 54$$ **Answer:** 54 adult tickets were sold.