John can service a television and a cable box in one hour. It took him four hours yesterday to service two televisions and ten cable boxes. How many minutes does John need to service a cable box?

For this item, we let x be the number of minutes he can service a television and y be the minutes he can service a cable box. Then, the system of linear equation that would best represent the given above is,

x + y = 60

2x + 10 y = (4) (60)

The values of x and y from the equations are 45 and 15 minutes, respectively. Therefore, John needs 15 minutes to service a cable box.