How much to charge to mow a yard that takes 3 hours?

It depends on how well you know the person and how well you do...If you know them well then ask for 5 dollars less and you'll get more...but overall probably 20-30 unless its the first time and its somebody you don't know...then say your doing the first one for half to see if they like it....they'll end up giving you more anyway...but always ask for less then you want....unless it's your parents..or relative..