c. \( c-(-3)=15 \)

To solve the equation \( c - (-3) = 15 \), you can start by recognizing that subtracting a negative number is the same as adding its positive counterpart. So, the equation simplifies to \( c + 3 = 15 \). Next, to isolate \( c \), subtract 3 from both sides, leading to \( c = 15 - 3 \), which gives you \( c = 12 \). Voila, you've found your value! When solving equations like this, one common mistake is misinterpreting the subtraction of a negative number. Always remember that \( -(-x) \) turns into \( +x \). Double-check your signs and operations to avoid pesky calculation errors!