An electrician sent Bonnie an invoice in the amount of 'a' dollars for 6 hours of work that was done on Saturday. The electrician charges a weekend fee 'f' in addition to an hourly rate 'r'. Bonnie knows what the weekend fee is. Write a formula Bonnie can use to find 'r', the rate the electrician charges per hour.

(a-f) / 6 = r

Step-by-step explanation:

The total Bonnie must pay is the weekend fee plus the hourly rate times the hours worked

Cost = weekend fee * hourly rate * hours

hours = 6

weekend fee = f

hourly rate = r

Cost = a dollars

Substituting in what we know

a = f + 6r

We want to solve for r

Subtract f from each side

a-f = f-f + 6r

a-f = 6r

Divide each side by 6

(a-f) / 6 = 6r/6

(a-f) / 6 = r