1. **State the problem:** Lilly thinks of a number $k$. She triples it and then subtracts 8 to get 7. 2. **Write the equation:** Tripling $k$ means $3k$. Subtracting 8 gives $3k - 8$. This equals 7, so the equation is: $$3k - 8 = 7$$ 3. **Solve for $k$:** Add 8 to both sides: $$3k - \cancel{8} + 8 = 7 + 8$$ $$3k = 15$$ Divide both sides by 3: $$\frac{3k}{\cancel{3}} = \frac{15}{\cancel{3}}$$ $$k = 5$$ 4. **Answer:** The number Lilly thought of is $k = 5$.