In a batch of steel columns, their lengths (L) were determined; where the length is a random variable with distribution

[answerhappygod]

In a batch of steel columns, their lengths (L) were determined;
where the length is a random variable with distribution N (μ; σ2).
It has been determined that there are 58% columns
with L ≤ 75, 38% with 75 < L ≤ 80 and 4% with L ≥ 80. (lengths
in inches)
a) Calculate the parameters of the distribution of L.
b) Calculate P (78 ≤ L ≤ 82).
c) Calculate the length in which 50% of the batch of steel columns
is located.