Answer:
a)
, n = 15 , X=3.4 , S=1.5 , α = .05
Formula : 


p- value = 0.607(using calculator)
α = .05
p- value > α
So, we failed to reject null hypothesis
b)
, n =75 , X=20.12 , S=2.1 , α = .10
Formula : 


p- value = 0.000412(using calculator)
α = .1
p- value< α
So, we reject null hypothesis
(c)
, n = 36, p-value = 0.061.
Assume α = .05
p-value = 0.061.
p- value > α
So, we failed to reject null hypothesis