Cont'd- How can I convince my parents to let me play Viola?

My last question was kinda unclear I guess... Im in the school band and I play the flute there, but I am going to continue flute... I want to play in the county strings orchestra recreationally. He, my friend, plays cello and is goin to a different high school next year. I just want to take up another instrument because I wanna learn alot of instruments and I have more opprotunities at scholarships........ Please Help!