formula for multiple cell percent total

Okay, it has probably been explained on here more than once and I apologize for that up front. I have been working to create a formula that in the end will pay an employee a different percentage depending on whether or not they drove their vehicle or the company vehicle on business. For instance, if the GROSS bill was $20 and PARTS were $5 and the employee drove THEIR vehicle, then, they would get 50% of the NET, in this case it would be $7.50. IF they drove a company vehicle, THEN they would get 40% of the NET or $6.00. Here is what I have and it does not work for me:

=IF(D5>0,(F5-G5)*0.4) (E5>0,(F5-G5)*0.5)

Where D5 is company mileage and E5 is personal mileage. SO, if they enter mileage in one cell or the other, it would figure the correct percentage. F5 is GROSS, G5 is PARTS. This would total out in H5

Thanks in Advance