"On line 9 schedule c Do I ADD the total cost of the trucks and the standard mileage rate with fuel?"

Have you done this before?

Vehicles are substantial purchases that have a useful life and are not "all gone" right away. That makes them Assets. Not Expense. Fuel, license, insurance, maintenance and supplies are examples of operating expense, because you use them up as you operate the vehicles. You cannot write off the purchase as Expense, because that vehicle is right there, still exists. Think of Asset as invested money, not Spent money.

Mileage allowance is the standard mileage rate for the use and operation of a vehicle when you don't need to detail the operating costs, for when the combined costs are taken into consideration by a mileage rate that covers it generically. For instance, mileage rate for operating a motorcycle for business is not the same rate as for a delivery van.

So, you really are asking about two separate things. Handling the new assets, and the already-owned assets. Then, handling the use of the assets - date placed in service, type of vehicle, weight, etc, are part of the IRS code for that type of vehicle as **bleep** groceries.

If you are doing the bookkeeping and not up to speed on these types of assets, you might want to pass this part to someone else. In this type of business, your client has a lot of $ riding on the correct treatment of their business vehicles.