From what I can see, you don't even have to work out the volume of the thing, so I'm not quite sure why they gave you the height.
Basically, you make a chord that is 25cm away from the radius. Then draw a line from the centre of the circle to each point where the chord meets the circle - forming an isoceles triangle, since both of these lengths are radii. Then if you draw a line down the middle, you know this line will be 25cm long (because the chord is 25cm away from the centre of the circle) and you know the hypoteneuse. By Pythagarous you should be able to work out half the length of the chord and hence the area of the chord.
I'll draw a diagram if you can't get it