1/2 Minus  what equals 7/8

Tom had a total of $220 and he spent $35 on a basketball ticket . what percent of his money did he have left?

Last month, a 770 g box of cereal was sold at a grocery store for $3.10. however, this month, the cereal manufacturer launched the same cereal in a 640 g box, which is being sold at $2.50. what is the percent change in the unit price?

What is the equation of a line passing through (-6,5) and having a slope of 1/3