Given the operation times provided:

a$.$ Develop a job sequence that minimizes idle time at the two work centers.

b$.$ Construct a chart of the activities at the two centers, and determine each one's idle time, assuming no other activities are involved.

$\backslash$table$[[,$JOB TIMES $($minutes$),,],[,$A$,$B$,$C$,$D$,$E$,$F$],[$Center $1,20,16,43,60,35,42],[$Center $2,27,30,51,12,28,24]]$