Please see question below: I understand how to compute part 1 but not part 2

Consider the following LP:

max 4x1+3x2+x3

st

2x1+4x2+x3<20

10x1+3x3<30

2x1+10x2+4x3<25

Add slack variables x4, x5 and x6.

In the final tableau variables x1, x2 and x4 are basic.

1)Using matrix methods compute the elements of the final tableau.

2) Using matrix methods compute the range for the cost coefficient of variable x1 within which the solution remains optimal.