martha pays $50 a month for the use of her cell phone. she also pays $0.30 for each minute that she talks over 6 hours. the cost of her phone billcan be represented by f(x)=50+0.30x, where x is the number of minutes past 6 hours that she uses the phone. evaluate f(60) to find the amount of her phone bill if she uses the phone for 7 hours.