From the present question, it was already given an equation that gives the amount of credit left as a function of the number of minutes used. Because of it, it only takes to substitute the wanted value, which in the present case is x = 50, in the equation, and perform the calculation, as follows:
[tex]\begin{gathered} C(x)=50.00-0.08\times x \\ C(50)=50.00-0.08\times50 \\ C(50)=50.00-4.00 \\ \\ C(50)=46.00 \end{gathered}[/tex]
From the solution developed above, we are able to conclude that, after 50 minutes of calls, there is a total of 46.00 dollars left.
From this, the answer you will need to type is just 46, or if it needs the cents also, you will type 46.00,
