Final Answer:
The correct equation to find the constant of variation (m) in this scenario is:

Explanation:
In the context of direct variation, the relationship between the two variables (cost, (c), and gallons, (g)) is expressed as ( c = mg), where ( m) is the constant of variation. To isolate ( m ) in this equation, we can rearrange it algebraically.
Dividing both sides of the equation by ( g ) gives:
![\[ (c)/(g) = (mg)/(g) \]](https://img.qammunity.org/2024/formulas/mathematics/high-school/g9g6u0r8002lpz4i67qe9xj2ienb2xjamk.png)
Simplifying the right side by canceling out the common factor of ( g ) leaves us with the desired equation:
![\[ (c)/(g) = m \]](https://img.qammunity.org/2024/formulas/mathematics/high-school/revn8mktd0aucfltgkasxg9ugp0a0iobq4.png)
This equation signifies that the constant of variation (( m )) is equal to the ratio of cost to gallons. In other words, it tells us how much cost changes for each additional gallon of gas. Therefore, the correct expression to find ( m) is ( c/g = m ).
Understanding the relationship between variables and the proper manipulation of equations is crucial in solving problems involving direct variation. In this case, recognizing that the constant of variation is obtained by dividing the cost by the number of gallons allows for an accurate and meaningful interpretation of the equation.