1. **State the problem:** Solve for $x$ in the proportion $\frac{5}{25} = \frac{x}{12}$.\n\n2. **Formula and rule:** In a proportion $\frac{a}{b} = \frac{c}{d}$, we can find the unknown by cross-multiplying: $a \times d = b \times c$.\n\n3. **Apply cross multiplication:** $5 \times 12 = 25 \times x$.\n\n4. **Calculate the left side:** $60 = 25x$.\n\n5. **Isolate $x$ by dividing both sides by 25:** $$x = \frac{60}{25}$$\n\n6. **Show cancellation of common factors:** $$x = \frac{\cancel{60}}{\cancel{25}} = \frac{12}{5}$$ (dividing numerator and denominator by 5).\n\n7. **Final answer:** $x = \frac{12}{5} = 2.4$.