Tickets for a football match are sold at $30 for adults and $15 for children a company bought 28 tickets if x of these tickets were for adults, write in terms of x a. the number of tickets for children b. the amount spent on tickets for adults c. the amount spent on tickets

First, we must let:
   x = number of tickets intended for adults
   y = number of tickets intended for children.

a. Write in terms of x the number of tickets for children
     Solution:
           x + y = 28   ⇔    y = 28 - x   (equation 1)
       To answer in terms of x:
           no. of tickets for tickets for children = 28 - x

b. the amount spent on tickets for adults
    Solution:  $30 is the cost of ticket per adult and there are x number of tickets intended for adults.
           Therefore, 
            amount spent on ticket for adults = 30x

c. the amount spent on the tickets.
     Solution:
       $ 15  = cost of ticket per child
       $ 30 = cost of ticket per adult

      total amount spent on tickets = 30x + 15y    ⇒   (equation2)
  substitute equation 1 to equation 2.
  (equation 1)   y = 28 - x
  (equation 2)   total amount spent on tickets = 30x + 15y
                        total amount spent on tickets = 30x + 15(28-x)
                        total amount spent on tickets = 30x + 420 - 15x
                        total amount spent on tickets = 15x + 420