Crystal 8.5 Summing question

In a one to many join How do you sum a field coming from the one table. example:
Table 1 has the following columns:
Employee id
check number
Gross pay
Table 2 has
Employee id
check number
ded code
ded amount
The data is as follows

employee id check number Gross Pay
1 1 100
1 2 100
1 3 100

employee id check number ded code ded amt
1 1 A 10
1 1 B 5
1 1 C 1

Each check would have the same 3 deductions.
When these tables are joined by employee id and check number you get a total of 9 records. If you wanted the total gross for the employee you can not just sum gross pay because you would get 900. The real gross for the employee should be 300.
I have been able to create a formula that gets the gross of 100 on one of the record and 0 on the other two records for each check, but Crystal will not let me sum that field.
Any help would be good.Try to create a Group on Employee ID so that it's not repeated. The records under an employee id will be displayed in Detail Section.

Create a summary field on gross pay and place it in Group Footer. this will returns the gross pay without duplication. To sum the check amout, create a separate sum field/running total field.

Hope this work.