A Ruby Laser Delivers a 2

A ruby laser delivers a 2.28-J pulse in approximately 50 nanoseconds.The wavelength of the light is 694.4 nm.At least how many atoms within the ruby rod had to be excited to allow this high-energy laser pulse? (h = 6.63 × 10−³⁴ J⋅s,c = 3.00 × 10⁸ m/s,1 eV = 1.6 × 10−¹⁹ J,and 1 nm = 10−⁹ m)

A) 3 × 10¹⁹
B) 4 × 10¹⁸
C) 8 × 10¹⁸
D) 6 × 10²⁰