9 to the second power:
9 x 9 = 81
Gas exchange occrs in the alevoli which are tiny air sacs in your lungs. the oxygen will then be carried off by capillaries which is part of ghe circulatory system.
EVERY fraction has a denominator. It's the number on the bottom.
We'll have to repeatedly square both sides of the equation, in order to get rid of the square roots. Squaring a first time yields

Move the 19 to the right hand side:

And square again:

Square one last time:

Let's check the solutions: all these squaring might have created external solutions:

So,
is a feasible solution.