Choice C is the correct answer. Let $M$ = Michael's age now and $C$ = cousin's age now.

System: $\begin{cases} M = C + 6 \\ (M - 4) + (C - 4) = 20 \end{cases}$

Step 1: Simplify second: $M + C - 8 = 20$$M + C = 28$

Step 2: Substitute: $(C + 6) + C = 28$$2C = 22$$C = 11$

Step 3: Find M: $M = 11 + 6 = 17$

Four years ago: $(18-4) + (12-4) = 14 + 8 = 22 \ eq 20$

💡 Strategic Tip: Age difference stays constant over time.