Aculture started with 2000 bacteria. after 8 hours it grew to 2400 predict how many bacteria will be present after 19 hours?

This is a geometric sequence but you don't know the growth factor, so you would solve for it first.

2400= 2000(x)^8

1.2= x^8

x= 1.02305188

You can round depending on what your teacher prefers. 
Now you can plug in your growth factor and solve.

A(19)= 2000(1.02305188)^19

A(19)= 2000(1.54189747739)

A(19)= 3083.79495477

After 19 hours, 3,084 bacteria will be present.