Question 2961
your problem is a very common one. i will show the steps below:

2x-5y=11
3x+y=8

multiply by 3 and -2
(3)2x-5y=11
(-2)3x+y=8

Now look carefully, and u'll find ur mistake:
6x-15y=33 --> you have to multiply the 2, the -5, and the 11 by 3, which u forgot
-6x+-2y=-16 --> likewise, u have to multiply the 3, 1,  and 8 by -2

from there, you just continue on the regular course of action, and u'll get the right answer.