At an Annual Growth Rate of 7 Percent, Real GDP $11_{1 / 2} \text { years. }$

At an annual growth rate of 7 percent, real GDP will double in about

A) $11_{1 / 2} \text { years. }$
B) 10 years.
C) $13_{1 / 2} \text { years. }$
D) 9 years.