$2.[4]$ Assume that we need to design a $2$G mobile system. The frequency band is shared by $4$ different service providers. The frequency band is divided into $250$ kHz channels for either uplink or downlink. Each frequency channel can support $8$ different time slots which can be used for voice or data services.

a$)[2]$ Suppose each service provider can have $49$ uplink channels and $49$ downlink channels, what is the total bandwidth $($uplink $+$ downlink$)$ of the frequency band we need?

b$)[2]$ Suppose every service provider applies frequency re$-$use in the cellular network, and divide its available frequency channels into seven groups for the re$-$use. Also, $5$ out of the $8$ time slots are used for voice calls. If the total number of mobile subscribers that can be supported at the same time for voice calls by all $4$ service providers is $112000,$ how many cells exist in the cellular network? $($You must show your calculations$).$