On the surface cost benefit analysis seems straightforward

The steps taken to evaluate each benefit and cost can become quite complicated. In this case, a benefit is defined as anything that increases human well-being, and a cost is anything that decreases it. These definitions and their respective calculations tend to provoke controversy due to the use of valuation.

In a chemical formula, the part to the left of the arrow represents the reactants. The reactants are all the chemical elements that will react with each others to make the products (which will be on the right part of the arrow).

Example:
H2 + O2 --> H2O

H2 and O2 are the reactants (on the left part of the arrow) and H2O is the product (on the right side of the arrow)

Hope this helps! :)