Maria wanted to bring back 5 million grains of sand from her trip to the beach. Each grain of sand weighs approximately 6.7 x 10^-7 kg. How heavy is the bag of sand that Maria brings home?

a
Multiply (5,000,000 x 6.7 x 10^-7) = (5 x 10^6) x (6.7 x 10^-7) = (5 x 6.7) x (10^(6 + - 7)) = 33.5 x 10^-1 = 3.35 kg
b
Multiply 5 x (6.7 x 10^-7) = 33.5 x 10^-7 = 3.35 x 10^-6 kg
c
Multiply (5,000,000 x 6.7 x 10^-7) = (5 x 10^6) x (6.7 x 10^-7) = (5 x 6.7) x (10^(6 + 7)) = 33.5 x 10^13 = 3.35 x 10^14 kg
d
Divide (5,000,000 / 6.7 x 10^-7) = (5 x 10^6) / (6.7 x 10^-7) = (5 / 6.7) x (10^(6 - 7)) = .74 x 10^-1 = 0.074 kg

PLEASE HELP