Step-by-step explanation:
I don't know if the first set of numbers is all in one set, but I'll do my best to give you an answer.
Really all you need to do is use PEMDAS for the first question.
(Parentheses, exponents, multiply, divide, add, subtract. In that order)

Then to simplify that fraction next to it, notice that 0.018 is 3x 0.06.
that's a 3:1 ratio, so it ends up simplifying to this:

Lastly, to solve the division of that fraction. If you divide by a fraction, you multiply whatever it's dividing by its inverse.
So...

7/8 in decimal form is 0.875 because you are dividing 7 by 8
Answer:
Mean=685
Variance=36.7
Step-by-step explanation:
The mean of uniform discrete distribution can be expressed as the average of the boundaries
mean=( b+a)/2
The variance of uniform discrete distribution can be expressed as the difference of the boundaries decreased by 1 and squared, decreased by 1 and divided by 12.
σ²=[(b-a+1)^2 - 1]/12
We were given the wavelength from from 675 to 695 nm which means
a= 675, b= 695
We can now calculate the mean by using the expresion below
mean=( b+a)/2
Mean=( 675 + 695)/2
=685
The variance can be calculated by using the expression below
σ²=[(b-a+1)^2 - 1]/12
σ²=[(695-675+1)^2 -1]/12
σ²=440/12
σ²=36.7
Therefore, the the mean and variance, of the wavelength distribution for this radiation are 685 and 36.7 respectively