How Long Does It Take Light to Travel Across the Width

Multiple Choice

How long does it take light to travel across the width of a Pb nucleus of radius 7.1 fm?

A) 2.4 $\times$ 10^-23 s
B) 1.2 $\times$ 10^-23 s
C) 2.4 $\times$ 10^-20 s
D) 4.7 $\times$ 10^-23 s
E) none of the above