Answer :
We can express the total payment as the product of the price of the bag, $6 per bag, and the number of bags, p (in this case, p is a variable that does not have an specific value yet).
Then, as p will have "bags" as unit, the product of the price ($/bag) and p (bag), will have "$" as unit.
a) We then can write:
[tex]C=6\cdot p[/tex]being C the total payment in $ and p the number of bags.
b) If the office spent $72, this means that C=72.
Then, we can find p as:
[tex]\begin{gathered} C=6p=72 \\ 6p=72 \\ p=\frac{72}{6} \\ p=12\text{ bags} \end{gathered}[/tex]Answer:
a) The total payment is equal to 6*p
b) They purchased 12 bags.