1. **State the problem:** This month’s commodity index is 60, which is one-quarter less than last month’s index. We need to find last month’s index. 2. **Set up the equation:** Let last month’s index be $x$. 3. Since this month’s index decreased by one-quarter of last month’s index, this month’s index is $x - \frac{1}{4}x$. 4. Simplify the expression: $$x - \frac{1}{4}x = \frac{4}{4}x - \frac{1}{4}x = \frac{3}{4}x$$ 5. We know this equals 60, so: $$\frac{3}{4}x = 60$$ 6. Solve for $x$ by dividing both sides by $\frac{3}{4}$: $$x = 60 \div \frac{3}{4}$$ 7. Dividing by a fraction is the same as multiplying by its reciprocal: $$x = 60 \times \frac{4}{3}$$ 8. Calculate: $$x = \frac{60 \times 4}{3} = \frac{240}{3} = 80$$ **Final answer:** Last month’s commodity index was 80.