Yes, the little bit of diesel won't harm the gas but make sure it's cleaned out before putting diesel back in as gas will harm a diesel. For more information please see the answer to the Related Question shown below.
regular gas
the 2012 mustang will run on regular gas
No
Diesel takes longer to burn than gas so, accordingly diesel is more fuel efficient.
Diesel gas gives more mileage (miles per gallon) than regular gasoline. You must, of course, have a vehicle that has a diesel engine because diesel fuel cannot be used in an engine that runs on regular gas! Depending on local government taxation policies, in some countries diesel is cheaper to buy than regular gas whilst in other countries it is more expensive! Diesel fuel is thicker and "stickier" than regular gas so, if a vehicle's fuel system ever needs cleaning - fuel tank, fuel lines, fuel pumps and fuel injectors - it is a more difficult and expensive job to do on a diesel vehicle.
Never put gas in a diesel car. And never put diesel in a gas car. An engine is built to handle one and not the other.
Yes, diesel trucks generally get much better gas mileage than regular gas trucks. They even sometimes get better gas mileage than hybrid trucks.
get that gas out of there as much as you can and then fill it with diesel a little regular gas will be ok and is ok to mix with diesel and will actauly clean it a little
Yes.
In most areas of the country Regular is not higher than Diesel, it is just the opposite.
Drain the tank, change the fuel filter, refill with diesel.
In a gasoline engine, definitely not. There are times when it is not inappropriate to add small amounts of gasoline to diesel for a diesel engine.