{1/3 x+ 1/4 y = 2 5x−y=11}

Please, when working with fractional coefficients, enclose them inside parentheses as shown here:

Correct:  (1/3)x + (1/4)y
Not clear:  1/3x+ 1/4y

Then we have:    (1/3)x + (1/4)y   and (2/5)x - y = 11.  (I must assume that your 2 5 meant 2/5.)

For clarity write this system as:

(1/3)x + (1/4)y = 2
(2/5)x - y = 11

The LCD of the first equation is (3)(4), or 12.  Mult. all three terms by 12 to clear the eq'n of fractions:        4x + 3y = 24

Go thru the same procedure for the second equation:  2x - 5y = 55

Now mult. the entire 2nd equation (immediately above) by -2 to obtain:

-4x + 10y = -110

and then add this to the first equation:

  4x + 3y = 24
-4x + 10y = -110
-----------------------
          13y = -86

Solving for y, y = -6.62 

It is unlikely that y would have a mixed number value.  Please, go back and check to ensure that you have copied down this problem correctly.  If you do, I'd be happy to return and help you find the solution of this system of equations.