Okay, here we have this:
Considering the provided information, we are going to find the requested equation, so we obtain the following:
Then we can see that we must find the function that represents the total cost, therefore we have
Total cost=Standard charge+ Insurance charge
Replacing:
C=0.50M+15.75+0.25M+5.80
C=(0.50M+0.25M)+(15.75+5.80)
C=0.75M+21.55
Finally we obtain that the equation for the total charge is C=0.75M+21.55