On the first day of a social media ad campaign, a website had 15 unique visitors. Over the following several days, the website received two times the number of unique visitors as the previous day.

Which equation can be used to determine the number of unique visitors, v, that the website would have on day d of the ad campaign?
Please only reply if you know the answer not just to get points I really need help
A) v= 15x2^d
B) v=2x15^d
C) v=2x15^(d-1)
D) v=15x2^(d-1)