Solve the problem.

Dub, Inc., is a small manufacturing firm that produces to microwave switches, switch A and switch B$.$ Each switch passes through two departments: assembly artd testing. Switch A requires $4$ hours of assembly and $1$ hour of testing, and switch $B$ requires $3$ hours of assembly and $2$ hours of testing. The maximum number of hours available each week for assembly and testing are $240$ and $140$ hours, respectively

a$.$ Define the variables and write inequalities to express reasonable values for the variables.

b$.$ Write an inequality to express the time restriction of the assembly department.

c$.$ Write an inequality to express the time restriction of the testing department.