S=5x+3y is revenue for ticket sales. So 5x+3y=1000 and x+y=300 for all seats filled. If all seats are filled we can write 3x+3y=900 and 3x+1000-5x=900, 100=5x-3x, 2x=100, x=50, so y=250. The revenue from adult ticket sales is $250 and from children's tickets is $750. If x=51 and y=249 the total revenue is 255+747=$1002; if x=49 and y=251, total sales=245+753=$998. If adults fill all the seats, the total sales=$1,500 (maximum); if children fill all the seats total sales=$900. So the break-even point is 50 adults and 250 children. If the number of adults is greater than 50, the sales will exceed $1,000 up to a maximum of $1,500 when only adults occupy the seats and all seats are occupied.