Hi! The interior degrees of triangles will always equal 360. Since two out of the three are 45°, this automatically means the third equals 90°. To find this, we set up an equations to look like this.
[tex]4x + 18= 90[/tex]
Now we'll subtract 18 from both sides.
[tex]4x = 72[/tex]
Divide both sides by 4 to solve for x.
[tex]x = 18[/tex]
