Refer to the Information Provided in Table 19 -Relating to the Economics in Practice on Page 392: Refer

Refer to the information provided in Table 19.1 below to answer the questions that follow.
Table 19.1
$$\begin{array} { | c | c | } \hline \text { Total Income } & \text { Total Taxes } \\\hline \$ 10,000 & \$ 1,000 \\\hline 20,000 & 2,400 \\\hline 30,000 & 4,500 \\\hline 40,000 & 8,000 \\\hline\end{array}$$
-Relating to the Economics in Practice on page 392: Refer to Table 19.1. If income increases from $30,000 to $40,000, the marginal tax rate is

A) 5%.
B) 20%.
C) 35%.
D) indeterminate from this information.