6. To host a children's party at an indoor playground, a family pays a non-refundable deposit plus an additional amount for each child attending. If \( 10 \) children attend, the total cost is \( \$ 380 \) . If \( 15 \) children attend, the total cost is \( \$ 440 \) .
(a) Write an equation to relate the total cost, \( C \) , to the number of children attending, \( n . ( 3 \) marks)