If the specific heat of water is 4.18 J/g⁰C and the specific heat of a rock is 0.418 J/g⁰C, how many grams of rocks at 200⁰C must be added to 100 grams of water to raise the water temperature from 20⁰C to 80⁰C? (Hint: the heat energy gained by water is equal to the heat energy lost by the rocks and both water and rocks have the same final temperature.) (Do not include units, round to the nearest whole number)