A quick mental shortcut is to double the 5% interest to get 10%, since this occurs over 2 years. Then taking 10% of something is the same as moving the decimal point one spot to the left. So we go from 200 to 20
since she has half a gallon and needs to split that between 18 dishes equally this means that 1/2÷18=1/36. each dish will have 1/36 of a gallon of salsa