Answer:
384.
Step-by-step explanation:
The population is given by the expression;

Where;
Y(t) is the number of bacteria at time, t.
P is the starting amount.
r is the growth rate.
Given that, P = 320, r = 20% = 0.2, t = 1
Substituting the parameters into the equation;

Y(1) = 320 * 0.2¹
Y(1) = 320 * 0.2
Y(1) = 64.
Therefore, the population of bacteria increases hourly by 64.
An hour later; 320 + 64 = 384.