GRE General Test: QR-961898 GRE Quantitative Reasoning

Keri, Neill, and Rich use toilet paper in their apartment in a ratio of 3:2:2. Rich buys two cases of toilet paper online for everyone’s use at 28 rolls per case, an average of $3.50/roll and a $14 delivery charge. If they each contribute to the cost of the toilet paper in direct proportion to the amount they use, how much must Keri contribute?