Challenge A cell phone plan costs $19.80 per month for 400 minutes of talk time. It costs an additional $0.06 per minute for each minute over 400 minutes. To get e-mail access, it costs 20% of the price for 400 minutes of talk time. Your bill, which includes e-mail, is the same each month for 6 months. The total cost for all 6 months is $168.48, Write and solve an equation to find the number of minutes of talk time you use each month.​