The perimeter of a rectangle is 2L + 2w (or the two lengths plus the 2 widths).
The area is Lw (that is, the length times the width).
Let's try making the two lengths 14 (or 7 apiece (14 / 2 = 7).
26 - 14 = 12, so the two widths are 12 (or 6 apiece (12 / 2 = 6)).
Area is the length times width, so 7 * 6 = 42
That's the area of one rectangle.
Let's try another one. Say, the two length is 18 (which means 9 apiece).
26 - 18 = 8, so the two widths are 8 (or 4 apiece).
9 * 4 = 36
42 > 36, so in this case the 7-length/6-width is the better of two options
Do note that they ask you to create your own rectangle, so the lengths/widths you end up with are your personal choices, so don't feel as if you have to use what I showed you here as the final say all.