Add the values of one Parent filed and on Child field and store the sum in another Parent field

1

Add the values of one Parent filed and on Child field and store the sum in another Parent field

The required information is given below :

Parent doctype :

image
image1501×559 42.5 KB

Child Doctype :

image
image1525×670 49.4 KB

Entries to the Parent doctype :

image
image1588×538 22 KB

Now I want to add Net Salary and in Incentives list the highest incentive i.e
2000 and store the value in Total Salary

Please help me out with this.