An internet company charges $12 per gigabyte of data plus a monthly service charge of $18. Last month, Niki's bill was $78. Write an equation to find how many gigabytes of data Niki used last month.
Let x represent the number of gigabytes of data Niki used.
Multiply the number of gigabytes by the cost per gigabyte. Add the service charge and set it equal to the price of the bill.