1. **State the problem:** Solve for $t$ in the proportion $$\frac{2}{5} = \frac{30}{3t + 9}.$$\n\n2. **Use the cross-multiplication rule for proportions:** If $$\frac{a}{b} = \frac{c}{d},$$ then $$a \times d = b \times c.$$\n\n3. **Apply cross multiplication:** $$2 \times (3t + 9) = 5 \times 30.$$\n\n4. **Simplify both sides:** $$2(3t + 9) = 150.$$\n\n5. **Distribute 2 on the left side:** $$6t + 18 = 150.$$\n\n6. **Subtract 18 from both sides:** $$6t + 18 - 18 = 150 - 18,$$ which simplifies to $$6t = 132.$$\n\n7. **Divide both sides by 6 to isolate $t$:** $$\frac{\cancel{6}t}{\cancel{6}} = \frac{132}{6}.$$\n\n8. **Simplify the division:** $$t = 22.$$\n\n**Final answer:** $$t = 22.$$