So first, you must use the area of an octagon formula to find the length of one side of the given octagon...
A = 2 ( 1 + √2) s^2
35 = 2 ( 1 + √2) s^2
s = 2.57 cm
Next, you must use the area of an octagon formula to find the area of the second octagon by multiplying the side length above by five.
A = 2 ( 1 + √2) s^2
A = 2 ( 1 + √2) (2.57 • 5)^2
A = 736.44 cm^2