The standard deviation of a proportion p is simply sqrt( p(1-p) ).

So here you have an estimated proportion = 0.9:

stdev = sqrt (0.9*0.1) = sqrt (0.09) = 0.3

For the second proportion, 30%, you have:

stdev = sqrt (0.3*0.7) = sqrt (0.21) = 0.46.

(Note that the question in the picture though doesn't ask you to compute the standard deviation, it wants you to make a histogram of the probabilities of r from 0 to 9)