Choice C is the correct answer. Let $T$ = Tom's age now and $B$ = brother's age now.

System: $\begin{cases} T = B + 4 \\ (T + 3) + (B + 3) = 30 \end{cases}$

Step 1: Simplify second: $T + B + 6 = 30$$T + B = 24$

Step 2: Substitute: $(B + 4) + B = 24$$2B = 20$$B = 10$

Step 3: Find T: $T = 10 + 4 = 14$

Solution: Tom is 14 years old

Verification: In 3 years: $(14+3) + (10+3) = 17 + 13 = 30$ ✓

💡 Strategic Tip: Age difference is constant over time.

**Other choices fail verification.