How to calculate to get profit

Does anyone have a good idea on how to tell if an order has earnings good enough to pick up?

I understand the mileage and all, but even with doing the math, it’s still confusing. What are your best ideas on how to tell if an order is worth picking up and driving for?

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Here’s the stats for the Spark nerds out there. Ignore it if you have a better way to calculate this:

I drive a van — 18 mpg city/23 mpg highway.

Fuel tank is approximately 25 gallons.

Gas prices are horrendous, so I’ve calculated that I would spend $4/gal in unleaded fuel. (Gas is $3.77/gal where I’m at.) Any extra money from the difference would be put towards maintenance.

I’ve calculated (18 mpg/$4 per gallon = 4.5 miles per $1 of gal.) that it would take this result to be enough to be worth taking the order, and completing it.

Even though Spark shows the total mileage of the order, that doesn’t include any miles put on the way to the Walmart where the order is picked up.