Acolony of 50 bacteria doubles in size every 170 minutes. what will the population be 680 minutes from now?

(not multiple choice)

Ok to start divide 680 by 170 which = 4

it doubles 50 each time so it would have doubled 4 times 50+50+50+50+50+50+50+50
  1   1   2    2     3   3     4    4

100       200      300       400

You know that total time is 680. The population doubles every 170
             680/170 = 4
The value of 4 means that the population will double four times or it goes through 4 iterations.

Initial Population  = 50 
1st iteration = 50 * 2 = 100     (it doubles the previous pop.)
2nd iteration  = 100 * 2 = 200   (it doubles the previous pop.)
3rd iteration =  200 * 2 = 400    (it doubles the previous pop.)
 4th iteration =  400 * 2 = 800    (it doubles the previous pop.)

Where is the picture