At the movie theatre, child admission is $5.10 and adult admission is $9.40 . on saturday, 158 tickets were sold for a total sales of $1184.20 . how many child tickets were sold that day?

Let children be x
Adult be y
5.10x+9.40y=1184.20 ... 1
x+y=158 ... 2

From 1// 510x+940y=118420 ... 3
From 2// y=158-x ... 4

Sub 4 into 3
510x+940(158-x)= 118420
510x+148520-940x=118420
-430x= -30100
x=70

As we know that children are x, 70 children tickets were sold.