First we have to convert miles to meters:
1 mile ≈ 1,609.34 m
Time of traveling one way:
\(t = \frac{240,000 * 1,609.34m}{3.00*10^{8}m/s } = \\ = \frac{8*10 ^{4} *1,609.34s}{10 ^{8} } = \frac{8*1,609.34 s}{10,000}\) = 1.28 s
From Earth to the Moon and back time is: 2 · 1.28 s = 2.56 s
