Part a is correct.
Part b can be done a couple ways.
1) Use binomial distribution. p = 0.2, n = 144
P(x>3) = 1 - P(x=0) -p(x=1) -p(x=2) -p(x=3)
where

2) Assume a normal distribution with mean = 28.2, stdev = 4.8

Look up z-value in normal table to find probability.
Hope that helps.
I've got it down to m+n=m*n but that doesn't seem to help. I'm still working
Let x = price of the bike before a sales tax.
The price after a sales tax of 8% is
x + 0.08x = 1.08x dollars
Because the price paid was $171.18, therefore
1.08x = 171.18
x = 171.18/1.08 = $158.50
Answer: 158.50
add them both then you get the awnser if the four is not a negative. if the four is a negative use division.