18. It would be the second graph. The third graph is eliminated as the boy takes a time period to shave, which means there should be a constant point (horizontal line) right after the first incline. The first one is eliminated as the boy takes a bath which requires another constant point in the graph.
19.
C
E
D
A
B

<span>Explanation for the last step:</span>
For this case we must find the product of the following expression:

We combine using the product rule for radicals:
![\sqrt [n] {a} * \sqrt [n] {b} = \sqrt [n] {ab}](https://tex.z-dn.net/?f=%5Csqrt%20%5Bn%5D%20%7Ba%7D%20%2A%20%5Csqrt%20%5Bn%5D%20%7Bb%7D%20%3D%20%5Csqrt%20%5Bn%5D%20%7Bab%7D)
So, we have:

We rewrite the 216 as

By definition of properties of powers and roots we have:
![\sqrt [n] {a ^ n} = a ^ {\frac {n} {n}} = a](https://tex.z-dn.net/?f=%5Csqrt%20%5Bn%5D%20%7Ba%20%5E%20n%7D%20%3D%20a%20%5E%20%7B%5Cfrac%20%7Bn%7D%20%7Bn%7D%7D%20%3D%20a)
Then, the expression is:

Answer:
Option D
5/8 inches longer since 8/8 - 3/8 = 5/8