Find equation in y=mx+b form from the context

The starting balance of Anna’s account is $1,250. She takes $30 out of her account each month. How much money is in her account after 1, 2, and 3 months? Find an equation to represent the balance in her account at any month.
  1. Use the description of the account balance to find the balance after each month.
  2. Determine the independent and dependent quantities.
  3. Determine if there is a common difference or common ratio that describes the change in the dependent quantity.
  4. Use the common difference to write an explicit equation.
  5. Evaluate the equation to verify that it is correct.