Pre algebra ( will give brainliest ) sorry if it's hard to see

If 3x+8=3x+8 is it one solution or no solution

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?

Me i'm timed right now! a. (0,-5)b. (0,-3)c. (0,3) d. (0,5)