Linear Programming - Simplex Method

Hi. I would like to get a FULLY WORKED solution of the following problem.

Maximize p = -x - y subject to

-x + 2y <= 4

3x + y <= 9

x >= 0

y >= 0

Initial starting point:

x=0

y=0

PS: I obtained the following solution from a website.

Tableau #1

x y s1 s2 s3 s4 p

-1 2 1 0 0 0 0 4

3 1 0 1 0 0 0 9

1 0 0 0 -1 0 0 0

0 1 0 0 0 -1 0 0

1 1 0 0 0 0 1 0

Tableau #2

x y s1 s2 s3 s4 p

-1 2 1 0 0 0 0 4

3 1 0 1 0 0 0 9

-1 0 0 0 1 0 0 0

0 1 0 0 0 -1 0 0

1 1 0 0 0 0 1 0

Tableau #3

x y s1 s2 s3 s4 p

-1 2 1 0 0 0 0 4

3 1 0 1 0 0 0 9

-1 0 0 0 1 0 0 0

0 -1 0 0 0 1 0 0

1 1 0 0 0 0 1 0

Sorry if this post is in the wrong forum!