3A +  5B = 10    (1)    (Monday)

    6A +  2B = 10    (2)    (Tuesday)


Multiply equation (1) by 2 (both sides).  Keep equation (2) as is.

You will get


    6A + 10B = 20    (1')    

    6A +  2B = 10    (2')    


Now subtract equation (2') from equation (1').

You will get

          8B = 10


Hence,  B =  =  hours = 1 hour and 15 minutes.


Then from equation (2),  2A = 10 - 6*(5/4}}} = 10 -  =  hours.


Hence,  A =  hours = 1 hour and 15 minutes.


ANSWER.  Both plans A and B are  1 hour and 15 minutes each for every individual client.