During 0-1 each task completes its initiate.

During 1-2
   Task 1 completes its request (i.e. the request is granted)
   Task 2's request cannot be granted (not safe).  So 2 is blocked
Three units available at 2.

During 2-3
   Banker first checks blocked tasks but cannot grant 2's request (not safe)
   task 1 completes its request.
No units available at 3.

During 3-4
   Banker first checks blocked tasks but cannot grant 2's request.
   task 1 releases four units (available at 4) and terminates at 4.
Four units available at 4

During 4-5
   Banker first checks blocked tasks and can grant 2's request.
Three units available at 5

During 5-6
   Task 2 completes its request
No units available at 6

During 6-7
   Task 2 releases fur units (available at 7) and terminates at 7.