Sam opened a savings account with $400. He earns $1,640 a
month at his job and will deposit 3% of his monthly pay every
month into his new savings account. Assuming he doesn't
withdraw money from his savings account, which equation shows
the balance y of his savings account x months after he opened it?
y = 12x + 400
y = 400x + 1640
y = 49.2x + 400
y = 0.03x + 400