Choice C is the correct answer. Let $b$ = bagels and $m$ = muffins.

System: $\begin{cases} b + m = 30 \\ 0.75b + 1.25m = 27.50 \end{cases}$

Step 1: Multiply second by 4 to clear decimals: $3b + 5m = 110$

Step 2: From first: $m = 30 - b$

Step 3: Substitute: $3b + 5(30 - b) = 110$$3b + 150 - 5b = 110$$-2b = -40$$b = 20$

Solution: 20 bagels

Verification: $20 + 10 = 30$ ✓ and $0.75(20) + 1.25(10) = 15 + 12.50 = 27.50$ ✓

💡 Strategic Tip: Multiply to eliminate decimals for easier calculation.