A manufacturing cell within a value stream is structured with four processes. The processes and their associated unit processing times are as follows:

$\backslash$table$[[$Cutting$,12$ minutes$],[$Drilling and inserion,$8$ minutes$],[$Assembly$,15$ minutes$],[$Finishing$,7$ minutes$]]$

Calculate the number of units the cell can produce per hour on a continuous running basis $($production rate$).$

a$.7$ units per hour

b$.3$ units per hour

c$.6$ units per hour

d$.4$ units per hour