Solution:
Take x as the number of child tickets sold, and y as the number of adult tickets sold.
so the equations will be:
6.30x+9.60y=1136.40 Equation 1 : Total sale.
x + y = 139 Equation 2: Total amount of tickets sold.
From equation 2, we obtain:
x = 139-y Equation 3
replacing this into equation 1, we get:
![6.30\mleft(139-y\mright)+9.60y=1136.40](https://img.qammunity.org/2023/formulas/mathematics/college/77hghvkddpmbhvmow1aum999x3koqva5sy.png)
applying the distributive property, this is equivalent to:
![875.7-6.30y+9.60y=1136.40](https://img.qammunity.org/2023/formulas/mathematics/college/jkas68jmag9deaq647u3c32ij4wcvt29qg.png)
this is equivalent to:
![-6.30y+9.60y=1136.40-\text{ }875.7](https://img.qammunity.org/2023/formulas/mathematics/college/j5z12tmpk8yp55fgjdsqw9veyilopowwq8.png)
this is equivalent to:
![3.3\text{ y = 260.7}](https://img.qammunity.org/2023/formulas/mathematics/college/bolqzifmy7kd18sol8q9ll6hqrl27p38fs.png)
solving for y, this is equivalent to:
![y\text{ =}(260.7)/(3.3)=79](https://img.qammunity.org/2023/formulas/mathematics/college/ebktw8q6mgxxjbx79yl32s7eg67mn8um85.png)
now, replacing this into equation 3, we obtain:
![x=139-y=\text{ 139-79=60}](https://img.qammunity.org/2023/formulas/mathematics/college/h4fu99tzr3ei41oipqf0f26xua9z6509q6.png)
So that, we can conclude that the correct answer is:
the number of child tickets sold is x= 60