Corrected the step 14 and step 16 of the first Chipotle problem

[AmineBellahsen]

Modified step 14 & step 16. Item price already takes into account the quantity. No need for "revenue" then. Thank you! :)

[dienluong]

Four years now and this correct solution is still not merged. (There are also several other steps in the current solution notebook that is far from optimal.)