Which expression is equal to 21,340?

a) 2.1343 x 10^4

b)0.2134 x 10^4

c) 0.2134 x 10^-6

d) 21.343 x 10^-4

To find the answer, move the decimal point over until you reach the final number. Move it to the right of that, and then count how many places you had to move over and write that as the exponent to 10. So the answer is A because you moved the decimal point 21640. <- here over 4 places, then you lose the zero. 

These are the multiples of 15 but what you are probably asking or what are the factors of 15