An operations analyst has gathered the following data on a fridge repair shop. design capacity of the shop is $120$ fridges, effective capacity of the shop is $80$ fridges, backlog in the system is $20$ fridges, actual service rate $67$ fridges for the past month, expected capacity was $90$ fridges, capacity in the system is $30$ fridges. Determine the effective utilisation of the fridge repair shop. a$)83\mathrm{.}8\%$ b$)88\mathrm{.}9\%,$ c$)75\mathrm{.}0\%,$ d$)66\mathrm{.}7\%$