Answer: 1.8 * 10^7
Reason
18 million = 18,000,000
We write "18" followed by 6 zeros.
Place a decimal point between the 1st pair of nonzero values (the 1 and the 8). So we get 1.8
How can we go from 1.8 back to 18,000,000?
We must move the decimal point 7 spots to the right. That "7" is the exponent over the 10.
Therefore,
