Answer:
There are 8 adults in the group.
Explanation:
Let the number of adults in the group be 'x'.
Given:
Number of children = 1
Number of adults = 'x'
Cost for a ticket of adult = $9
Cost for a ticket of a child = $6
Total cost = $78
Total cost is equal to total cost of tickets of 'x' adults plus cost of ticket of 1 child.
Unit cost of 1 adult × Number of adults + cost of ticket of 1 child = Total cost
Framing in equation form, we get:
![9x + 6 = 78](https://img.qammunity.org/2021/formulas/mathematics/high-school/nnc8uzt9yqozib1syy5kvy9fmc1pludwmq.png)
Adding -6 on both sides, we get:
![9x=78-6\\\\9x=72](https://img.qammunity.org/2021/formulas/mathematics/high-school/5gcdoqr4bqpihhs9mjaukwgfjo93e8y0q6.png)
Dividing both sides by 9, we get:
![x=(72)/(9)=8](https://img.qammunity.org/2021/formulas/mathematics/high-school/2udci73uogellmr811wv2s32i150vn07cq.png)
Therefore, there are 8 adults in the group.