The equation for a circle is pi x radius x radius. So,first we need to find the radius which is half the diameter, 140 divided by 2 equals 70 cm. As the question asks for the answer as a multiple of pi there is no need to multiply by pi. So the answer is simple 70 x 70 which without a calculator it would be easier to do 7 x 7 which is 49 and then add the two zeros on at the end, giving 4900. Therefore the answer would be 4900pi cm^2.