If a phone card is used to make a long distance phone call, you are charged $0.50 per call plus an additional $0.31 per minute. part a: write an equation that can be used to find the total cost of a phone call that lasts for m minutes. part b: shalon was charged $5.15 after using a phone card to make a phone call. for how many minutes did he talk on the phone? show your work.