Each week Mr. Jones goes to the grocery store. This week he bought 10 pounds of fruit and spent $15.60. Last week, he bought exactly the same amount of the same fruit and spent $11.70. Find the percent of change and state whether there was a decrease or increase. please help

Mrs. morton has a special reward system for her class. when all her students behave well, she rewards them by putting 3 marbles into a marble jar. when the jar has 100 or more marbles, the students have a party. right now, the the jar has 24 marbles. how could mrs. morton reward the class in order for the students to have a party?