Those two each account for 12.5%. If both are heavily polluted, then heavily polluted = 12.5%*2=25%.

Mass = 1-25%-25%=50%, which can actually be seen as half of the whole circle.

Total number =40/ 12.5%=320, mass =320*50%= 160.

So the ratio of heavy pollution to light pollution = 25%: 25%: 50% =1:1:2.

hope this helps