The circumference is merely increased by 50%. The formula for a circle (which I assume you know) is 2*pi*r. Work out this value, then multiply it by 1.5. You get the same answer as multiplying 2*pi*(r*1.5). Just fyi (if you didn't know), multiplying something by 1.5 increases it by 50%, multiplying something by 1.12 increases something by 12% etc.
