ANSWER
The volume of the dilated cube is 9375cm³.
EXPLANATION
The volume of the original cube is 75 cm³.
The scale factor for the dilation is 5.
The scale factor for volume is 5³=125
We multiply the volume of the original cube by 125 to obtain the volume of the dilated cube.
The volume of the dilated cube is

Answer:
No solution
Step-by-step explanation:
We have

For the sum it is not correct to assume

Note that for

it is assumed
and in your case
for 
In fact, considering a set
we have
that satisfy 
This means that, by definition 
Therefore,

because the sum is empty.
For

we have other problems. Actually, this case is really bad.
Note that
has no value. In fact, if we consider for the case
, the cosine function oscillates between
, and therefore it is undefined. Thus, we cannot evaluate

and then

has no solution
You use the lower case letter s for the sample standard deviation
You use the greek letter sigma (written as

) for the population standard deviation