Please answer I need step by step explanation

How many $20 bills do you need to have to make $280

Sara can take no more than 22 pounds of luggage on a trip.her suitcase weighs 112 ounces.how many more pounds can she pack without going over the limit?

Campus rentals rents 2 and 3 bedrooms apartments for $700 ans $900 a month respectively. last month they had six vacant apartments and reported $4600 in lost rent. how many of each type of apartment were vacant?