Step-by-step explanation:

This involves quite a lot of arithmetic to do manually.
The first thing you do is to make the first number in row 2 = to 0.
This is done by R2 = -3/2 R1 + R2
so the matrix becomes
( 2 1 1) ( -3 )
( 0 -13/2 3/2) (1/2 )
(5 -1 2) (-2)
Next step is to make the 5 in row 5 = 0
then the -1 must become zero
You aim for the form
( 1 0 0) (x)
(0 1 0) (y)
(0 0 1) ( z)
x , y and z will be the required solutions.
No, because, using the Pythagorean Theorum:
6^2+8^2=9^2
36+64 IS NOT = TO 81
Answer:
I) 54.2 X 94 = 5094.8
J) 36.39 X 28 = 1018.92
K) 43.73 X 74.4 = 3253.512