You need some specific information. How many batteries does Tina have? How many power cells are there in each battery? How many power cells does the radio burn in one minute?
Divide the number of power cells in one battery by the number of cells the radio burns in one minute to figure out how long before a single battery dies.
The total length of time Tina can use the radio is longer than the time she would have with only 1 battery. How many minutes does she have before all 3 of the batteries die?
