With these, you pick either equation and a variable to solve for; let's solve for x using the 2nd eq: 3x - 4y = 11; 3x = 4y - 11; x = (4/3)y - (11/3).
Now, plug x into the first eq: 3( (4/3)y - (11/3) ) + 4y = 5; 4y -11 +4y = 5; 8y = 16; y = 2.
To get an actual number for x, plug in y into either equation and you should get x = -1.