Demand for residential electricity at $6$:$00$ p$.$m$.$ on the first

Monday in October in Santa Theresa County is normally

distributed with a mean of $4,905$ MW $($megawatts$)$ and a

standard deviation of $355$ MW$.$ Due to scheduled maintenance

and unexpected system failures in a generating station,

the utility can supply a maximum of $5,200$ MW at that

time. What is the probability that the utility will have to

purchase electricity from other utilities or allow brownouts?