1. **State the problem:** Zander has 18 coins total, consisting of dimes and quarters, with a total value of 3.90. 2. **Define variables:** Let $d$ be the number of dimes and $q$ be the number of quarters. 3. **Write equations:** - Total coins: $$d + q = 18$$ - Total value in dollars: $$0.10d + 0.25q = 3.90$$ 4. **Solve the system:** From the first equation, express $d$ as $$d = 18 - q$$ 5. Substitute into the value equation: $$0.10(18 - q) + 0.25q = 3.90$$ 6. Simplify: $$1.8 - 0.10q + 0.25q = 3.90$$ $$1.8 + 0.15q = 3.90$$ 7. Isolate $q$: $$0.15q = 3.90 - 1.8$$ $$0.15q = 2.10$$ 8. Divide both sides by 0.15: $$q = \frac{2.10}{0.15}$$ $$q = \cancel{\frac{2.10}{0.15}} 14$$ 9. Find $d$: $$d = 18 - 14 = 4$$ **Final answer:** Zander has 4 dimes and 14 quarters.