Now let's look at triangles.
  How many sides does a triangle have.... 3 right?

However,  there are many different types of triangles...
Here are the definitions of each...  (click on the image to enlarge)

  A triangle has three sides and three angles.

All of the angles add up to 180 degrees.  Here is an example...

45°+90°+45°= 180°
Note:  ° means degrees

What if you were given an equation like this?

One can see we have 85° and 55°.  We do not have x.

To find x you need to first add up these two numbers
85°+55°= 140°

All triangles equal 180° total :)
So...

Take the 140° and minus it from 180°
180°-140°= 40°

The ANSWER:  X= 40°