Is the error when they flipped the 28/6 ?

When dividing by a fraction you flip the second fraction over and change to multiply.

The error was simplifying the -36 and the 28

That shouldn’t have been done. After flipping the fraction over they should have multiplied across:

-36/1 x 6/28 = (-36 x 6) / (1 x 28) = -216/28

Rewrite as: -7 5/7

chemists are often responsible for designing a chemical reaction and analyzing the products obtained from it. one significant part of designing a chemical reaction is determining the amount of each reactant that is needed and the amount of each product that will be produced. in order to do so, chemists use stoichiometry, the quantitative relationships between reactants and products.