The Following Are Costs of Advertising (In Thousands of Dollars)and $\begin{array} { c | r r r r r r r r } Cost & 9 & 2 & 3 & 4 & 2 & 5 & 9 & 10 \\\hline Number & 85 & 52 & 55 & 68 & 67 & 86 & 83 & 73\end{array}$

Multiple Choice

The following are costs of advertising (in thousands of dollars) and the numbers of products sold (in thousands) : $\begin{array} { c | r r r r r r r r } Cost & 9 & 2 & 3 & 4 & 2 & 5 & 9 & 10 \\\hline Number & 85 & 52 & 55 & 68 & 67 & 86 & 83 & 73\end{array}$
The equation of the regression line is $y = 2.78846 x + 55.7885$ . Find the coefficient of determination.

A) $0.2353$
B) $0.5009$
C) $0.7077$
D) $- 0.0707$