The answer is k = 15. A straight line is 180 degrees. L to Y is a ray which is a line. And M to X is a straight line. So the interior angle Y is the same as 4k+5 as well as 6k+10.
So your equation would look like this...
180=115+4k+5
180=120+4k
-120 -120
60=4k
60/4= 4k/4
15=k
