The formula for finding the area of a circle is
Pi x radius^2
Therefore, you've got to divide 237.787 by Pi (which is 3.142 to 3 decimals)
237.787/3.142= 75.68 to two decimal places.
As this is then the radius squared, you then need to find the square root.
Sq root of 75.68= 8.71.
As the radius is half of the diameter, you've then got to double this, which gives you 17.42
Therefore, the diameter is 17.42
Hope this helps :)