Problem $1\mathrm{.}3$: A work group of $20$ workers in a certain month produced $8600$ units of output

working $8h\frac{r}{?}$ day for $21$ days. $($a$)$ What is the labor productivity ratio for this month? $($b$)$ In the next

month, the same worker group produced $8000$ units but there were $22$ workdays in the month and

the size of the work group was reduced to $14$ workers. What is the labor productivity ratio for this

second month? $($c$)$ What is the productivity index using the first month as a base?