Acircular pond is to be surrounded by a gravel path to find the square feet of gravel needed if we know the pond has a radius of 200 ft and the radius of the whole space is 250 ft

So we can just subtract the area of the pond from the area of the whole space.
So to find the area of the pond, 
200².
That would equal about 125663.7 ish.
And then the whole area would be
250².
That would equal about 196349.541
And then just do
196349.541 - 125663.7 = 70685.741 ish
So they would need about 70685.741 square feet of gravel.