Answer:
see the explanation
Step-by-step explanation:
Let
x ----> number of usage days
y ---> the total charge monthly in dollars
we know that
The linear equation in slope intercept form is equal to

where
m is the slope or unit rate
b is the y-intercept or initial value
In this problem we have


substitute

we have the ordered pair (13,41)
For x=13 usage days


therefore
That means----> Total charge in one month for 13 days of use is $41