I need to know how to do this and step by step.

The formula for the area of a circle is PI r (square) or 3.14 * r^2 or 3.14 * r * r, all are the same thing. For 49, they give you the radius is 6.2 ft.
49.
3.14 * 6.2 * 6.2 = 120.7 ft(squared)
50.
diameter = 11 yards
Means: Radius = 5.5 yards (radius is half of a diameter)
3.14 * 5.5 * 5.5 = 94.99 yards ft(squared)
Now just round these values to the nearest tenth if not done so already. 94.99 will be 95.0 rounded to the nearest tenth.