Notice how the circle touches both the left and right edges of the square. That given length, 38", creates the diameter of the circle.
To find the area - πr² - you'll need r, the radius, which you can find by splitting the diameter in half, getting a radius of 38/2 = 19".
Using 3.14 as an approximation for π, we get an area of (3.14)(19)² = (3.14)(361) = 1133.54 in²