Hi
Yes, it is possible by sharing the values using Shared Variables :
--Go in your sub report 1 and create a formula like :
Whileprintingrecords;
Shared Numbervar Val;
val:= {equip.qty}*{equip.price};
In Sub report 2
Whileprintingrecords;
Shared Numbervar Val1;
val1:= {material.qty}*{material.price}
In sub report 3
Whileprintingrecords;
Shared Numbervar Val2;
val2:= {manpower.qty}*{manpower.price}
Now create formula in your main report like :
WhileprintingRecords;
Shared numbervar val;
Shared numbervar val1;
Shared numbervar val2;
Numbervar Total;
Total:=val+val1+val2;
This will display the total of above three sub report formulas.