Suppose Sarah Owns a Small Company That Makes Wedding Cakes

Suppose Sarah owns a small company that makes wedding cakes. The accompanying table shows how Sarah's total cost varies depending on the number of wedding cakes she makes each day. $$\begin{array} { | c | c | } \hline \text { Number of Cales Per Day } & \text { Tatal Cast Per Day } \\\hline 0 & \$ 100 \\\hline 1 & \$ 180 \\\hline 2 & \$ 220 \\\hline 3 & \$ 300 \\\hline 4 & \$ 400 \\\hline 5 & \$ 520 \\\hline 6 & \$ 660 \\\hline\end{array}$$  
The marginal cost of the 4ᵗʰ wedding cake per day is ________.

A) $100
B) $120
C) $300
D) $400