Construct a frequency table with equal class intervals from the following data on the monthly wages (in rupees) of `28` labourers working in a factory, talking one of the class intervals as `210-230` (`230` not included):
`220,268,258,242,210,268,272,242,311,290,300,320, 319,304,302,318,306,292,254,278,210,240,280,316,306, 215,256,236`

A ground frequency table with class intervals of equal sizes using 250-270 (270 not included in this interval) as one of the class interval is constructed for the for the following data 268,220,368,258,242,310,272,342, 310, 290, 300, 320, 319, 304, 402, 338, 406, 292, 354, 278, 210, 240, 330, 336, 406, 215, 258, 236. The frequency of the class 310-330 is