Major arc jl measures 300°.

which describes triangle jlm?

right
obtuse
scalene
equilateral

It would be equilateral.
Since major arc JL is 300, then the minor arc is 60 degrees.
That makes angle M 60 degrees because it is a central angle so equal to the intercepting arc.
Since the other two angles of the triangle are equal (both legs of the triangle are radii so are equal), the other two angles must also be 60 degrees.
If all three angles are 60 degrees, it is an equilateral triangle (all angles add to 180).