margaret purchased a new bar of soap. three days after she originally used the soap, she was curious how much soap per day she was using. she decided to weigh her soap and found that the bar was 103 grams. four days later she re-measured the same bar of soap and recorded a weight of 80 grams. assuming that margaret uses the same amount of soap daily (and that she used the soap daily), write an equation that shows the amount of soap remaining after d days of use.