Every morning Mr C makes coffee for his wife Ms F. He carefully measures 15 grams of ground coffee into his aeropress, puts the aeropress and cup on a kitchen scale, zeros the reading, and adds 200 grams of water at 97C from a temperature controlled kettle.

One day he mistakenly uses 18 grams of coffee (the dose he normally uses for espresso).

a) How many grams of water should he use to achieve the same concentration of coffee? b) Suppose instead of 18 he used 20 grams of coffee. How many grams of water should he use in this case? c) In general, how many grams of water should be used for each gram of coffee?