Since you asked how to solve this, I will put the answer at the bottom.
You might not think the same way as I but I think in steps.
<h3>(1) Calculate how many times the bacteria divide in eleven hours</h3>The bacteria divide every 20 minutes, and will therefore divide three times every hour, 60/20 = 3.
If the bacteria grow for eleven hours, each bacterium will divide 3 times per hour × 11 hours = 33 times.
<h3>(2) Add the orginial size of bacteria into the equation</h3>(This part is edited)
(orginial size)*2^number of divisions
10*
=85899345920