Three people become infected with a virus that spreads quickly. each day that passes, the number of infected people doubles. how can the number of infected people be determined from the number of days that have passed?

a: raise the number of days to the second power, and then multiply this value by 3.
b: add the number of days to 3, and then multiply this sum by 2.
c: multiply the number of days by 2, and then add 3 to this product.
d: raise 2 to the number of days, and then multiply this value by 3.