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.