[Algebra]
Problem: Let T be a rational number, and let $K=T-2$. If $K$ workers can produce 9 widgets in 1 hour, compute the number of workers needed to produce $\frac{720}{K}$ widgets in 4 hours.

Solution: Because $T$ workers produce 9 widgets in 1 hour, 1 worker will produce $\frac{9}{T}$ widgets in 1 hour. Thus 1 worker will produce $\frac{36}{T}$ widgets in 4 hours. In order to produce $\frac{720}{T}$ widgets in 4 hours, it will require $\frac{720 / T}{36 / T}=\mathbf{2 0}$ workers (independent of $T$ ).

Final answer: 20