The situation described can be modeled by a linear function.
In a linear function, the relationship between the variables is constant and can be represented by a straight line on a graph. In this case, as Sarah's visits to the chiropractor increase, her fees decrease by a fixed amount of $5 each time. This means that there is a constant rate of change between the number of visits and the corresponding decrease in fees.
Let's say the number of visits is represented by the variable 'x' and the fees by the variable 'y'. The relationship can be expressed as:
y = mx + b
Where 'm' represents the rate of change (in this case, -5 because the fees decrease by $5) and 'b' represents the initial fee or the y-intercept.
Therefore, the situation of Sarah's fees decreasing by $5 each time she visits the chiropractor can be modeled by a linear function.