$1.$ Compute the capacity $($i$.$e$.$ processing rate$)$ for each of the following scenarios. Convert your answers to parts per hour.

a$.$ A four$-$station line with single$-$machine stations, where the average processing times are $15,20,10$ and $12$ minutes, respectively.

b$.$ A three$-$station line where the number of machines at stations $1,2$ and $3$ is $2,6,$ and $3,$ respectively; and the average processing times are $10,24$ and $18$ minutes, respectively.