The answer is 267.
If we wanted to represent this scenario as an equation, it would be 22.40-14+.5x (x being the amount of texts after 250). We are using PEMDAS, but because the variable is unknown, we skip multiplication and just go left to right. 22.40 - 14 = 8.40. With 8.40, we now know how much it costed AFTER 250 messages (how much she owes after $14). If we want to find how many PER 50 cents, we have to DIVIDE (reverse of multiplication). 8.4 / .5 = 16.80. Because you can't send .8 of a text message, you round to get 17. 250 + 17 = 267 (messages sent that month).