Inverse variation:

k is a constant
Use the given information (when x=4 y=4) to find the value of the constant:

Then, the given relationship has the next equation:

Use the equation above to find y when x=2:

Then, when x=2, y=8
Because if you multiply 2 different irrational numbers (like the following)

You will get an irrational answer.
BUT
if you multiply the same square root (which are both irrational, you get a rational number)
Answer:
no
no
no
yes yes
Step-by-step explanation:
not 100% but it should be right
so 21 - 13, the money will be invested for 8 years.
