Marty opened a savings account to deposit a portion of his monthly salary. Without considering interest earned, his savings account is modeled by the function f(x) = 300x + 500. How much money did Marty initially deposit? A) Marty's initial deposit was $0. B) Marty's initial deposit was $300. C) Marty's initial deposit was $500. D) Marty's initial deposit was $800.