Find the value of two numbers of their sum is 144 and their difference is 22

We just started the introduction into circles and i have no idea how to do this.

I’m still confused on how to work the percentages

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?