-The Table Above Gives a Nation's Investment Demand and Saving

$$\begin{array} { c c c c c } \begin{array} { l } \text { Real interest rate } \\\text { (percent per year) }\end{array} & \begin{array} { c } \text { Investment } \\\text { (billions of }\end{array} & \begin{array} { c } \text { Private saving } \\\text { (billions of }\end{array} & \begin{array} { c } \text { Net taxes } \\\text { (billions of }\end{array} & \begin{array} { c } \text { Government expenditures } \\\text { (billions of }\end{array} \\\text { 2005 dollars) } & \text { 2005 dollars) } & \text { 2005 dollars) } \\\hline 3 & 60 & 20 & 40 & 20 \\4 & 50 & 30 & 40 & 20 \\5 & 40 & 40 & 40 & 20 \\6 & 30 & 50 & 40 & 20 \\7 & 20 & 60 & 40 & 20\end{array}$$
-The table above gives a nation's investment demand and saving supply schedules.It also has the government's net taxes and expenditures.When the real interest rate is 4 percent, the supply of loanable funds is equal to

A) $80 billion.
B) $30 billion.
C) $50 billion.
D) $90 billion.
E) $10 billion.