I'm assuming the deck is the shaded area.
To find the area of the deck, find the area of the large circle and subtract the area of the small circle from it:
A of large circle: R = (4.2/2) + 1.7 = 3.8; area: 3.8^2 * pi is about 45.3.
A of small circle: r = 4.2/2 = 2.1; area: 2.1^2 * pi is about 13.8
Now, subtract:
45.3 - 13.8 = 31.5 meters squared