Abank's monthly charge for maintaining an account is $.45 for each check written plus a service charge of $12.50. if x represents the number of checks written during the month, which function models this situation? a) f(x) = x + 12.50 b) f(x) = 0.45x -12.50 c) f(x) = 12.50x + 0.45 d) f(x) = 0.45x + 12.50