Note: <em>The question states the time to go upstream is a number of times (not explicitly written) the time to go downstream. We'll assume a general number N</em>
Answer:

Explanation:
<u>Relative Speed</u>
If a boat is going upstream against the water current, the true speed of motion is
, being
the speed of the boat and
the speed of the water. If the boat is going downstream, the true speed becomes
.
The question states the time to go upstream is a number of times N (not explicitly written) the time to go downstream. The speed of an object is computed as

Where x is the distance traveled and t the time taken for that. The time can be computed by

If
is the time for the upstream travel and
is the time for the downstream travel, then

Siince the same distance x= 10 miles is traveled in both cases:

Simplifying and rearrangling

Operating

Solving for 



If N=3

We can use the required value of N to compute the speed of the boat as explained
Answer:
1. The compound should be dissolved at the solvent boiling point.
2. It should be better none of the compound dissolve while at room
temperature.
3. The compound must have lower boiling point (low boiling point) than
melting point in hot solvent so to avoid it melts.
4. The compound have different solubility and impurity.
Explanation:
in order a compound to have a good crystallization, these are the primary consideration that should be followed.
1. The compound should be dissolved at the solvent boiling point.
2. It should be better none of the compound dissolve while at room
temperature.
3. The compound must have lower boiling point (low boiling point) than
melting point in hot solvent so to avoid it melts.
4. The compound have different solubility and impurity.
Answer:
Iris
Explanation:
The iris seems to be the illuminated portion of the eyes which really covers the pupil. It controls the amount of light reaching the eye. The lens is indeed a translucent layer of the retina that serves to concentrate light and objects on the lens.