Answer:
420 boards.
Explanation:
We have been given the formula for cost per board as
, where x represent number of boards. We are asked to find the number of boards that must be sold to limit the final cost per board to $215.
To find the number of boards, we will equate cost of x boards by 215 and solve for x as shown below:








Therefore, 420 boards must be sold to limit the final cost per board to $215.