Mathswatch hw need help

In the diagram below what is the approximate length of the minor arc ab

Find dy/dx using implicit differentiation ln(20+e^xy)=y

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?