Jkl is an equilateral triangle and km and jl

Line KM bisects the equilateral triangle, which halves Angle K. 

Because all angles of an equilateral triangle are 60, we can divide the original angle of K by 2 to find the new angle:



Angle K is 30 degrees.

Triangle JKM has two angles of 90 and 30. Angle M is 90 degrees, as it has the square defining the angle, and Angle K is 30 degrees. Angle J has remained unchanged, so it is 60 degrees. This makes Triangle JKM a 30-60-90 triangle.

The answer is B.