so you subsitute 275 for n in the equation
becaue the question says 'let n represent the number of text messages'
so .15(n-250)+5=.15(275-250)+5
so we do the stuff in the parenthasees () first so .15(25)+5
multiply by .15 or 15/100 so
and you get 3.75
3.75+5
you add 5 and get 8.75