(a)
The class width of the histogram is given by the range of each bar in the histogram, that is, the upper limit minus the lower limit of a bar (plus 1, since we need to include the boundary values of the range).
Looking at the first bar, the upper limit is 19 and the lower limit is 11, therefore the class width is 9 (because there are 9 elements between 11 and 19, so we need to add 1 to the subtraction of 19 and 11)
(b)
The most frequent class is the third one (third vertical bar).
The frequency of this bar (that is, the value in the y-axis) is equal to 8.
Therefore 8 women are in this class.
(c)
The number of women with 28 or fewer blouses is given by the frequency of the first two bars.
Adding the frequency of the first bar (1) and the frequency of the second bar (5), we have that 6 women have 28 or fewer blouses.