Kris forwards an e-mail to 5 people. each of those people forward that e-mail to 5 more people. if this happens two more times, which expression shows the total number of people who have received the e-mail, not including kris?

a) 4 x 5
b) 1+5+5^2
c)5+5^2+5^3
d) 5+5^2+5^3+5^4

The answer is D. It can't be A, because that would be if 4 people forwarded it to 5 people each. It can't be B, because that would be Kris, the people she forwarded it to, and the people they forwarded it to, it can't be C, because that the people Kris forwarded it to, the people they forwarded it to, and the people they forwarded it to, it's missing the 4th round of people. So it must be D.