Of means multiplication
So

And then simplify the numerator ad denominator
=

And simplify the numerator and denominator again
=

And we are finally left with the answer which is
Answer:
0.025
Step-by-step explanation:
Α = 1- (95/100) = 1-0.95 = 0.05
p = 1- α/2 = 1- 0.05/2 = 1-0.025 = 0.975
Degrees of freedom, df = Sample size -1 = 11-1 = 10
From t-tables, with cumulative probability pf 0.975 and df of 10,
Critical value = 2.228
X = 12 inches so D is correct