There are four resources and four jobs to be done. Assume there must be one$-$to$-$one matching between jobs and resources. The time required for each resource to do each job is as follows:

$\backslash$table$[[,$Job $($Hours$)],[$Resource$,$A$,$B$,$C$,$D$],[1,5,8,7,7],[2,4,9,5,9],[3,6,9,8,7],[4,7,6,6,9]]$

For the optimal schedule, what is the total number of hours required to complete these jobs?

Multiple Choice

$20$ hours

$22$ hours

$19$ hours

$21$ hours

$23$ hours