Question

Please help, I don't understand how to do this.

Answer 1

The interior angles of a triangle all add up to 180 degrees.
You know two of those angles. They are 26 degrees and 90 degrees. The little square thingy in the corner means that angle is 90 degrees.

Using the info above, you can set an equation for the missing angle INSIDE the triangle. Please keep in mind, the x in this equation does not represent angle L.
26+90+x=180
116+x=180
x=64

Now that we know the missing angle inside the triangle, you can find angle L. Angle L and the angle we just found are supplementary, because they are on a line. Supplementary means they add up to 180 degrees.

So, you can make an equation.
64+L=180
L=116

Angle L is 116 degrees. Sorry for the long answer!