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Here is an example, but always remember that you can only use elimination when the variables have different signs..

3x - 4y = 10
9x + 4y = 26
now eliminate -4y and 4y since they have different signs what's left is
3x = 10
9x = 26
add like terms will result to
12x = 36
solve for x buy dividing both side by 12 and the result is x=3

now to solve the value of y substitute the value of x to any of the equation here i'll take 9x+4y=26

substituting the value of x to the equation
9(3) + 4y = 26
27 + 4y = 26
       4y = 26 -27 (by transposition process)
       4y = 1
         y = 1/4 (dividing both side by 4)

hope this would help