Answer:
To find the ratio of grains of sand on Earth to stars in the galaxy, we divide the number of grains of sand by the number of stars: (7.5 x 10^18 grains of sand) / (4 x 10^11 stars).
To divide these numbers, we subtract the exponents: (7.5 x 10^18) / (4 x 10^11) = (7.5/4) x (10^18/10^11) = 1.875 x 10^7.
Therefore, there are 1.875 x 10^7 times as many grains of sand on Earth than stars in the galaxy.
The correct answer is B) 1.875 x 10^7.