A 9-month-old is brought to the emergency center by ambulance. The child had been having emesis and diarrhea with decreased urine output for several days, and the parents noted that she was hard to wake up this morning. Her weight is 9 kg, down from 11 kg the week prior at her 9- month checkup. You note her hea rate and blood pressure to be normal. She is lethargic, and her skin is noted to be "doughy." After confirming that her respiratory status is stable, you send electrolytes, which you expect to be abnormal. You sta an IV. The best solution for an initial IV bolus would be