Delta calculation per ID

Hi everyone, I have dataset which contains the info of Sprints. Some tasks get spilled over to the next sprint due to incompletion of the task.The dataset contain TaskID,Task,completed work and Sprint fields. But the completed work field has the cumulative data for the spilled over Tasks.Example: Consider Task A and Task B, Task A worked upon in 2 sprints which are  March and April.In March, lets say i spent 100 hours ​. In April i spent 50 more hours, but the value is 150hrs ​. Ideally effort for April, I need to consider only 50,Which means I need to do 150 (Effort in April) -100 (Effort in March). Task B does not get spilled over,Task B is  worked upon in 1 sprint which is March,let say effort spent is 50 hours. So the Completed work will be same as 50. I want to create a calculated column which has the delta value for the spilled over tasks and  the same value for not spilled over tasks.Like Task A and Task B should have values in calculated column as 100,50 and 50 respectively.
 
Thanks,
Mahesh