According to the meaning of the question, the sum of seven groups of rectangular areas from left to right is 0.94, and the sum of seven groups of frequencies from left to right is 0.94.

The frequency of the last group is 1-0.94=0.06,

It is known that the frequency of the previous group is 12, and the sample size of this sampling is12 ÷ 0.04 = 200;