Explanation:

Let the time taken Ram alone to complete the work be ‘x’ days.
Time taken by Amit alone to complete the work = x*0.80 = 4x/5 days
Time taken by Deepka alone to complete the work = x/1.5 = 2x/3 days
1/x+5/4x+3/2x = 1/8
=> x = 30
Time taken by Amit and Deepak alone to complete the work = 4x/5 = 24 and 2x/3 = 20 resp.
Required time together by Amit and Deepak = 1/[(1/24)+(1/20)] = 120/11 days

OR 

D: R :A

12:8:10

BY RATIO METHOD .

NOW , work = 30x 8=240

now effencies of deepak and amit = 12 + 10 = 22

=> 240 / 22

120/11