What could be the approximate expected distribution of light?

Classic example of natural selection is the change in relative populations of the peppered moth that occurred during the industrial revolution in England. After the industrial revolution in 1870s, booming industrial cities started releasing tons of black soot, blackening tree trunks and rocks 
and creating an environment where moths with light colours were easily predated by birds. Peppered moths captured in 1850 and 1900 reveal that two industrial cities (X and Y) had the following percent distributions. Year 1850 and 1900.

Moths   Light coloured   Dark coloured   Light coloured     Dark coloured
X                  66                34                 22                  78 
Y                  65                 35                27                  73

Pollution control rules were introduced in 1902 and were properly followed in city Y, but not in city X. If all other factors remain constant, then what could be the approximate expected distribution of light and dark coloured moths in 1950?