Originally Posted by aico

You need to work on your English before you delve into Mathematics.

I don't even think you know what you fucking asked...

When you say "If 30% off is $13.00, what is the full price", that means that the new price after a 30% discount is $13.00, which made the original price $18.57.

Try to stay with me here:

Off = subtract
is = equals

so what you asked was basically "If Subtracting 30% = $13.00, what was the full price?"

If you wanted the answer to be the 43.33 your question should have been "30% OF the full price is $13.00, what is the full price?"