How to get the last column value from the child table

I am trying to get the last column value of the child table ,where i want to get the value of Basic and add a value to it which i got a filed name value_difference

supposed that the last columns value is 71311.61 ,so after save ,the value of value_differece should get added to it ie 71311.61+1,079.19=8210.61

this value should be should to that particular row

is there any way to achieve this?

Try using client script.