Histogram

Can someone explain why 3 blocks are equal to a frequency of 6, when I counted there were 18 blocks so surely each block would have a frequency of just one.

The question is attached

If Ive understood it, the histogram is frequency density
https://www.bbc.co.uk/bitesize/guides/zspfcwx/revision/1
The solution looks right although very poorly explained.

How do 18 blocks equal a frequency of 6 what is the steps behind this.
I do 20 x 0.4 = 18 this means that the graph is proportional to the table. As the frequency of the first data set is 18.
What am I doing wrong here?

For the first bar, the frequency density is 40 = 18/0.45 (frequency/width).
it youre happy with that, ignore the model answer and just do the other categories (bars).

I get the answer that
The frequency of the first blank in the table is 18
I did this by multiplying 60 X (0.75-0.45) = 18

And the second is 6
I did this by multiplying 20 X (1.05 - 0.75) = 6

Is this correct?
Because the answer on the attached file is different