Given 10x = 4, find x

Mr and mrs smith buy tickets for themselves and their four children. the cost of an adult ticket is ? 6 more than the adult ticket. the total cost of the six tickets is ? 40.50 work out the cost of an adult ticket. in your working let c be the cost of the child ticket and a be the cost of the adult ticket.

How can i differentiate this equation?

Aof 12 , we to a of 4 to on a .of 4 be ?