ANS:D - 10 shovels and 24 dumpers on days 3 and 4

Activity 1-2 and 1-3 are parallel activity and run parallel for 2 days as the duration for 1-2 is 2 days so for this time no of shovel required =1+3=4.

And no of dumper reqd =4+8=12.

Now, activities 1-2 finish after 3 days and 1-3 continue with 2-3 and 2-4 for the remaining 2 days.
So no of shovel reqd=3+4+3=10.
No dumper required =8+4+12=24.

After 1-3 is complete activity 2-3 and 2-4 runs for 2 days as after 2 days activity 2-3 will finish.

So, no of shovel reqd= 4+3=7.
No of dumper reqd=4+12=16.

In a similar manner requirement of shovel and dumper can be computed for remaining activities.

Thanks.