What value of x makes this equation true? 15-7x=5x-21

Ahigh definition tv cost $800 with a down payment of 2/5 of the cost. how much is left to pay, in dollars after the down payment has been made?

There are 4 cups in a quart and 4 quarts in a ganon.jug of water? . how many cups are in a 5-gallon jug of water?

20.ju inces. which ordered pair is a viable solution if x represents the number of books he orders and y represents the total weight of the books, in ounces? (-3,-18) (-0.5, -3) (0,0) (0.5, 3)