For typographical reasons, brackets around matrices are omitted here.

1.
To get the matrix of T, make the given columns into the columns of a matrix:

2 5 0
3 1 4

2.
Once [A | 1] is in RREF and becomes [1 | B], B is the inverse of A. So the answer is the right half of the second matrix, i.e.

-51    21    2
   29 -12 -1
   -2      1    0

3.
The product is

2(0) + 1(-1)      2(3) + 1(1)
1(0) + 3(-1)      1(3) + 3(1)

or

-1 7
-3 6

which is also the matrix of SU (the matrix of the composition is the product of the matrices).