Sekeping gambar foto berbentuk segi empat tepat mempunyai luas $(23 + 17\sqrt{2})$ cm² dan lebar $(3 + \sqrt{2})$ cm. Cari beza antara panjang dan lebar, dalam cm, gambar foto itu. Beri jawapan anda dalam bentuk surd.

A rectangular photograph has an area of $(23 + 17\sqrt{2})$ cm² and a width of $(3 + \sqrt{2})$ cm. Find the difference between the length and the width, in cm, of the photograph. Give your answer in surd form.