H = hardcover books
Paperback books = twice the harcover books = 2H
Original number in the collection = H + 2H = 3H
Books checked out = H + x(3H/9) where x is the number of members checking out the paperback books
Paperbacks returned = 2(3H /9)
Paperbacks not returned = (x - 2)(3H/9)
So we have this equation
Books in collection = [ books returned ] + [ books not returned ]
3H = [2 (3H/9)] + [ H + (x - 2)(3H/9) ] simplify
3H = [ H(2/3) ] + [ H + (H)(x - 2)/3 ] divide through by H
3 = (2/3) + 1 + (x - 2)/3
3 = (2/3) + 1 + (x - 2)/3 multiply through by 3
9 = 2 + 3 + x - 2
9 = 3 + x
9 - 3 = x
6 = x
You need to make 5 calls.....one to Member 7427 and (x - 2) = (6 - 2) = 4 more to those who checked out the unreturned paperbacks