Can someone please help me solve this?

The sum of the reciprocal of a positive number and the reciprocal of 2 more than the number is 3/4 equation: the number is

How do you use the elimination method for this question? explain, because i really want to understand!

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?