How is (s-t)(s/t) equivalent to (s^2/t) -s

The monthly texting plan of all star cell is $11 per month and $0.25 per text. the monthly texting plan of top line cell is $14 per month and $0.15 per text. a student wants to set up a system of equations to find the number of texts for which the total monthly cost of the two companies is the same. he uses the variables x and y. he lets y represent the total monthly cost. what will x represent? x = number of texts x = cost of the total number of texts x = total monthly cost x = cost of each text