Use angle of section 3 to get ratios of arcs:Realise either one of the arcs 1 or 2 will do.Calculate 360-30 / 3 to get 110 degrees for section 1.Calculate ratio of arcs for section 1: 11/36
Find pi:Multiply arc1 length by 36/11 to get total perimeter.Divide by diameter: 2x30cmGet 3.141818... > 3.14