If a certain type of bacteria quadruples every 15 minutes, how many bacteria will be presents after 90 minutes if the initial population was 5 bacteria? me for 97 points

For this case we have an equation of the form:
 y = A (b) ^ (t / n)
 Where,
 A: initial amount
 b: growth rate
 t: time
 n: number of time periods
 Substituting values we have:
 y = 5 * (4) ^ (90/15)
 y = 20480
 
 will be presents after 90 minutes about:
 y = 20480 bacteria