1) x+12,4=15,82 2) x-8,5=-8,5
3) 16,2+x=-7,2
4) x:4+11=10
5) x:(-10)+20=11
6) 9-3x=x+20
7) 7+(3x-8)=-8
8) 3x-(x-1)=-7
9) 5(1-x)=2(x-8)
10) 3(x+1)=-2(1-x)+6​

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?