last thread for the night

lastthread for the night, thanks if you can help me with these last problems

In the formula A=lw, If l is constant, A varies___________ as w

A large concrecte mixing machine can mix a certain ammount of concrete in 12 hours, while a smaller one can mix the same ammount in 20 hours, Mixing simultaneously, how long would it take both machines to mix the same ammount of concrete?

For a school play, students tickets cost 40cent and adult tickets were 75 cen t. The total receipts for 90 tickets were $46.50. How many of each kind were sold?