The width of a hydrogen atom is 5 × 10–8 mm (millimeters). If the moon is 3.7 × 106 km (kilometers) from Earth, how many times the width of a hydrogen atom is the distance from the earth to the moon?
I have taken the liberty of rewording your question. Is this what you meant?
The width of a hydrogen atom is 5 × 10^(–80 mm (millimeters). If the moon is 3.7 × 106 km (kilometers) from Earth, how many hydrogen atoms will fit in a row between the earth and the moon.
i don't know about hydrogen atoms but the distance to the moon is closer to 384400km which is much further than 3.7*106.
Anyway
3.7 x 106km = 3.7 x 106 x 1000 x 1000 mm = 392.2 x 1000000 mm = 3.922 x 10^8
3.922 x 10^8 / 5 x 10^(-8) = 7.844 x 10^15
+118654 
