Question $2$: Find order quantity using Single Period ModeL.

Lambton College usually sells $120$ copies of the Operations Management book each semester.

Chris believes the sale of the book is normally distributed, with a standard deviation of $15$ books. Lambton pays $70$ cents for each book, which sells for $$1\mathrm{.}25.$ The publisher gives Lambton a $30-$cent credit for each unsold book at the end of the semester.

Determine how mary books Lambton should ordes each semester.