Answer:
A= I think because it is definite not c so there is a solution differently I know so that is my final answer.
Sorry if I am wrong.
I believe the formula to find the height would be h= 2a/b and if you use that formula and plug in the area (21.7) of each triangle as well as the base (6) then you would get a height of 7.2 cm. I hope this is correct! :)
Answer:
Step-by-step explanation:

Sum/difference:
Let

This means that

Now, assume that
is rational. The sum/difference of two rational numbers is still rational (so 5-x is rational), and the division by 3 doesn't change this. So, you have that the square root of 8 equals a rational number, which is false. The mistake must have been supposing that
was rational, which proves that the sum/difference of the two given terms was irrational
Multiplication/division:
The logic is actually the same: if we multiply the two terms we get

if again we assume x to be rational, we have

But if x is rational, so is -x/15, and again we come to a contradiction: we have the square root of 8 on one side, which is irrational, and -x/15 on the other, which is rational. So, again, x must have been irrational. You can prove the same claim for the division in a totally similar fashion.