Hi Muhammad,
I've put your question in matrix form (first column is A, second column is B, third column is C, fourth column is D, fifth column is E and the last is the constant term). I find it a little easier to write a question like this as an augmented matrix.

Here is your question in matrix form

I subtracted the first row to the thrid row, put the result in the thrid row

I multiplied the last row by 2 then added it to the first row, put the result in the last row 
I multiplied the thrid row by 4 then added it to the last row, put the result in the last row 
I switched the first and second row. 
I divided the second row by 2, the thrid row by 2 and the last row by 4 
I multiplied the last row by 3/2 and then added it to the thrid row, I put the result in the thrid row

I multiplied the last row by 2 then added it to the second row, I put the result in the second row

I subtracted the second row from the first row and put the result in the first row 
Now the matrix is in row echelon form.
We can see that A=3/8, B=C, D=3/8 and E =1/4. Note that B can be any number and C is the negative of B. 
Check out "An Augmented Matrix" for further help
Hope this helps,
Janice
