Choice B is the correct answer. Let $g$ = goats and $d$ = ducks.

System: $\begin{cases} g + d = 45 \\ 4g + 2d = 126 \end{cases}$

Step 1: From first: $d = 45 - g$

Step 2: Substitute: $4g + 2(45 - g) = 126$$4g + 90 - 2g = 126$$2g = 36$$g = 18$

Solution: 18 goats

Verification: $18 + 27 = 45$ ✓ and $4(18) + 2(27) = 72 + 54 = 126$ ✓

💡 Strategic Tip: Animals/legs problems are classic systems applications.

**Other choices fail verification.