You can only do it like '7.5 plus 9.5 plus 13
Let x = number of adults tickets sold
then, 1750 - x = number of children tickets sold
We know that the cost for adult tickets is $5 and and children is above calculated so sum total tickets sold cost is $7100.
($5)(x) + ($2)(1750-x) = $7100
5x - 2x + 3500 = 7100
3x = 3600
x = 1200
