1st column = price of books
2nd column = no. of books sold. = -1032*1st column+38440
3rd column = cost of books = 4.9*2nd column
4th column = profit = 3rd column - 2nd column*1st column.
is the equation to the max profit. after putting 1,2,3,4 together.
after rearranging and simplify.
then to find max. you differentiate the equation to
to find x
hence the max profit = $21
please ask questions if you dont understand as i havent explain it fully.