Which of the following uses the reciprocal property to rewrite x/5 = 72/4

Please help me :)

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?

10x − 5y + 14 = 0 whats the answer pls

Sam opened a money-market account that pays 3% simple interest. he started the account with $7,000 and made no further deposits. when he closed the account, he had earned $420 in interest. how long did he keep his account open?