The phone costs $930, and he already has $320 saved in his bank account so subtract 320 from 930. You will get 610. Then, you take 610 and divide it by 20 because he earns $20 a week. I hope this helped.
You have to use the equation which has just slipped my mind. It say x1-y1 over x2-y2. Then you will find x. I am so sorry this equation name slipped my mind. If I remember I will let you know.
