Jamie's Marginal Utility from Muffins and from Doughnuts (In Utils)

Jamie's marginal utility from muffins and from doughnuts (in utils) is shown below. Jamie spends a total of $8 on muffins and/or doughnuts every morning. The price of each muffin is $2 and the price of each doughnut is $1. $$\begin{array} { | c | c | c | c | } \hline \begin{array} { c } \text { Muffins } \\\text { Per Day }\end{array} & \begin{array} { c } \text { Marginal Utility } \\\text { Per Muffin }\end{array} & \begin{array} { c } \text { Doughnuts } \\\text { Per Day }\end{array} & \begin{array} { c } \text { Marginal Utility } \\\text { Per Doughnut }\end{array} \\\hline 1 & 40 & 2 & 20 \\\hline 2 & 30 & 4 & 15 \\\hline 3 & 20 & 6 & 10 \\\hline\end{array}$$ If Jamie consumes 2 doughnuts a day, then what is her marginal utility per dollar spent on the second doughnut?

A) 10
B) 15
C) 20
D) 40