An electron has an atomic mass of 5.4 x 10-4. if a carbon atom has 6 electrons, what is the combined atomic mass of the electrons in a single carbon atom? answer in scientific notation.

a) 3.24 x 10-3
b) 3.24 x 10-4
c) 3.24 x 10-5
d) 32.4 x 10-4

6*5.4*10^(-4)
=32.4*10^(-4)
move the decimal point, in scientific notation you only have a single digit with comma
=3.2*10^(-3)

so option A

to know if you have to increase or decrease the exponent you can write the intermediary steps out:
32.4*10^(-4)=32.4/10^4=(3.24*10)/(10*10^3)
reduce the fraction and you have the above solution

What are the choices