Chris portable radio can operate for 7.15 hours on one 9 volts if chris has 8 new batteries how many hours can he operate the radio

Your awnser would be 57.2 hours

57.2 hours because you have to find how much of the battery the radio will use for one hour then you multiply the amount of battery the radio will use by 72 because there are 8 batteries times 9 volts which gives you 72 volts.