With number 27 can you explain how u got the answer

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

If you make you answer for clear i can answer it : )