We know how to make 18 gm. How many 18s do we need to get to 140?
How much of A do you need to get 2 gm of X? 10 gm / litre so...
How much of B do you need to get 16 gm of Y? 15 mg / cm^3 ==> 15 gm / litre so...
Liquid A has 10 grams of element X per liter. Liquid B has 15 milligrams of element Y per (there are 1000 milligrams in a gram and 1000 in a liter). It is desired to make 140 grams of molecule Z. To make 18 grams of Z requires 2 grams of X and 16 grams of Y. How many liters of each liquid should be used?