What is the sum of all 4 digit numbers that can be formed by the digits 0 , 1 , 2 , 3 , 4 ? No repetitions allowed .
`` How do I Simplify the following matrices : 1 . -5 -LSB- -7 0 0 5 -RSB- ; 2 . 3 -LSB- 6 4 5 -5 3 1 -RSB- ? ''