#6. Let the number of adults is a and the number of children is c.
The total number of people is 42,
a+c=42......(1).
The sales made by selling tickets is $396,
12a+8c=396.....(2)
Thus, the above two equation gives the required system of equation for the problem.
#7.
The system of equation can be solved as by substituting the value of c from (1) in (2),
Thus, a=15.
Now susbstituting the value of a in equaiton (1),
#8.
Thus, number of adults in the therater is 15 and number of children in the theatre is 27.