How do I solve for X HELP

Jenisey has $24 to spend on seven pencils. after buying them she had $10. how much did each pencil cost.?

Barbara deposited $300 in the bank. if the bank pays her simple interest at the rate of 4 percent per year, how much money will she have in her account at the end of 9 months?

You got a job selling magazines door-to-door. you are paid $100 per day plus $1.50 for each magazine you sell. which recursive formula models this situation?