1. **State the problem:** Solve for $c$ in the equation $2.5 + \frac{c}{0.4} = 11$. 2. **Isolate the term with $c$:** Subtract 2.5 from both sides: $$2.5 + \frac{c}{0.4} - 2.5 = 11 - 2.5$$ $$\frac{c}{0.4} = 8.5$$ 3. **Solve for $c$:** Multiply both sides by 0.4 to cancel the denominator: $$\cancel{0.4} \times \frac{c}{\cancel{0.4}} = 8.5 \times 0.4$$ $$c = 3.4$$ 4. **Final answer:** $c = 3.4$. This means that when $c$ is 3.4, the original equation holds true.