The base ball diamond has the dimensions of a square. See the diagram in the attachment.
Therefore the area is given by the formula

We were given the area to be 3600 feet squared. We just have to substitute this value into the formula to obtain;

Taking the positive square root of both sides gives;

Thus implies that;

We can also rewrite this as;

The distance between each base is how far one side is from the other. This is equal to the perpendicular distance between them and this is the same as the length of the sides.
