4. In cell I4, enter a formula that uses the IF function and structured references to calculate customer sales Growth (as a %).
a. Growth can be calculated if the value in the 2015 Purchases column is greater than 0.
b. To calculate Growth (as a %), divide the value in the Growth ($) column by the value in the 2016 Purchases column.
c. If the value in the 2015 Purchases column is not greater than 0, return a value of N/A. If necessary, copy the formula you created in cell I4 to the range I5:I27.