College algebra, I’m really bad at word problems. Please help.

Question

The population of bacteria is directly proportional to the temperature. There are about 10 million bacteria at 20 degrees Celsius. 

Create a formula for this. What type of variation is this? What is k? How many bacteria will there be at 30 degrees celsius? Where else would I use this?

Answer 1

10/20 = B/30

1/2 = B/30

B =30/2 = 15 million when temperature is 30 degrees

B = T/2

the number of bacteria in the millions = half degrees

it's direct variation

B= kT

where k= 1/2