1. **State the problem:** We have two phone plans with different cost structures. We want to find the number of minutes where the total cost of Plan A equals the total cost of Plan B. 2. **Define variables and write equations:** Let $x$ be the number of minutes of calls. - Plan A cost: $21 + 0.13x$ - Plan B cost: $0.17x$ 3. **Set the costs equal to find the break-even point:** $$21 + 0.13x = 0.17x$$ 4. **Solve for $x$:** Subtract $0.13x$ from both sides: $$21 = 0.17x - 0.13x$$ $$21 = 0.04x$$ Divide both sides by $0.04$: $$x = \frac{21}{0.04} = 525$$ 5. **Interpretation:** The two plans cost the same when you use 525 minutes. 6. **Find the cost at 525 minutes:** Use either plan's formula, for example Plan B: $$\text{Cost} = 0.17 \times 525 = 89.25$$ **Final answers:** - Minutes: $525$ - Cost: $89.25$