Help pls if its linear or nonlinear

Terri makes a quilt using three sizes of fabric squares the side lenght of each fabric square is the square root of the area

Which expression is equivalent to -5(3x - 6/7)

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?