On paper just switch the numerator and denominator of 3/5 to get 5/3 and then just multiply across (numerator by numerator and denominator by denominator) to get 55/9, which on a calculator gives 6.111111... so rounded about 6.
I can't really explain this, but you should you the desmos scientific calculator, just look it up. For other fractions too, you can turn into decimals, and then divide from there which is easier for me.
