The square root of 8 is also irrational.
Well first you change x - 2y = .9 to x = .9 + 2y, by adding y from both sides of the equation. Then, you substitute x=.9 + 27 into 4x - 3y = 13.1 to get 4(.9 + 2y)- 3y= 13.1. Use the distrubutive property and you get 4 * .9 = 3.6 and 4 * 2y = 8y. Now you have 3.6 + 8y - 3y = 1...
which object will have higher inertia a rock of 20kg or a hollow ball of 22kg