Let's formulate an equation first. For exponential growth, we follow the formula. b = 800, r - 0.027. Hence,
y = 800(1+0.027)^t
Then, at t = 21, y will be determined
y = 800 (1+0.027)^21
y = 1399.81 = 1400
Thus, the amount of bacteria present after 21 hours is 1400.