I would say a. Good luck!
To minimize the material usage we have to have the volume requested with the minimum surface area.
The volume is:

And the surface is:

From the first equation we get:

I will use k instead of a number just for the conveince.
We plug this into the second equation and we get:

To find the minimum of this function we have to find the zeros of its first derivative.
Sx will denote the first derivative with respect to x and Sy will denote the first derivative with respect to Sy.

Now let both derivatives go to zero and solve the system (this will give us the so-called critical points).

Now we plug in the first equation into the other and we get:

Now we can calculate y:

And finaly we calculate z:

And finaly let's check our result:
Answer:
the seed of the sound in the air is 343.3 m/s
Explanation:
The computation of the speed of the sound in the air is shown below:
As we know that
Speed = Distance divided by Time
So, here speed be 515m
And, the time is 1.50 second
So, the speed of the sound is
= 515m divided by 1.50 seconds
= 343.3 m/s
hence, the speed of the sound in the air is 343.3 m/s
No because it is dense and opaque