.
Part (a)
This problem is a binomial distribution with the parameters
n = 4 (the number of trials);
k >= 2 (the number of success);
p = 0.2 (the probability of individual success).
The probability is
P = P(2) + P(3) + P(4) = P(n=4, k>=2, p=0.2) = = .
To facilitate my calculations, I used online calculator at this site https://stattrek.com/online-calculator/binomial.aspx
It provides nice instructions and a convenient input and output for all relevant options/cases.
The resulting number is P = 0.1808 (rounded). ANSWER
Part (a) is complete.
Part (b)
The binomial distribution has the following properties:
The mean of the distribution (μx) is equal to n * P = 4*0.2 = 0.8.
The variance (σ2x) is n * P * ( 1 - P ) = 4*0.2*0.8 = 0.64.
The standard deviation (σx) is sqrt[ n * P * ( 1 - P ) ] = = 0.8.
For the reference, see this web-site
https://stattrek.com/probability-distributions/binomial#:~:text=The%20binomial%20distribution%20has%20the,(%201%20%2D%20P%20)%20%5D.
or your textbook.
Part (b) is complete.