The value of y is in the triangle is 2
In the triangle MB is the bisector of line JB and BK this means that JB is equal to BK and line MB is equal to line Line MB.
Therefore we can say that triangle JMB and KMB ate congruent.
If this triangles are congruent, this means that line JM is equal to line MK
therefore;
12y - 18 = 3y
collect like terms
-18 = 3y - 12y
-18 = -9y
divide both sides by -9
y = -18/-9
y = 2
Therefore the value of y in the triangle is 2