## Marbles in a Cup

**Work Time**

# Marbles in a Cup

Chen has some marbles that are all identical.

He puts 12 marbles in a cup. The marbles and the cup together have a mass of 147 grams.

When he puts 15 marbles in the cup, he finds that the marbles and the cup together have a mass of 165 grams.

Let *n* = the number of marbles in the cup. Let *m* = the mass of a marble in grams. Let *c* = the mass of the cup in grams.

- Write a formula for
*w*, the mass in grams of the cup and the marbles together, using just the variables but no numbers. - What is the mass of the cup in grams? Show how you got your answer.