The Following Table Shows the Amount Spent, in Billions of Dollars

The following table shows the amount spent, in billions of dollars, on recreational boats and accessories in the United States during the period 1999-2001. (Let S be the set of all dollars represented in the table.)
Compute the cardinality of the set described as $n ( A \cap ( N \cup U ) )$ . $$\begin{array} { | l | l | l | l | l | } \hline & \text { Used Boats, } \boldsymbol { U } & \text { New Boats, } \boldsymbol { N } & \text { Accessories, } \boldsymbol { R } & \text { Total } \\\hline \mathbf { 1 9 9 9 , } , \boldsymbol { A } & 5 & 7 & 3 & 15 \\\hline \mathbf { 2 0 0 0 } , \boldsymbol { B } & 7 & 7.5 & 2 & 16.5 \\\hline \mathbf { 2 0 0 1 } , \boldsymbol { C } & 8 & 8 & 5 & 21 \\\hline \text { Total } & 20 & 22.5 & 10 & 52.5 \\\hline\end{array}$$ ​
​ $n ( A \cap ( N \cup U ) ) =$ __________ billion dollars.