there are a dozen ways in order to solve this, however, the simplest would probably be an application of law of sines combined with definition of interior angles of triangles.
the sum of interior angles of a triangle is 180 degrees, you're given that one angle is 45 degrees and another is 90 degrees, thus the missing angle is 45 degrees
now, Law of Sines states,
[tex]\frac{sin A}{a} =\frac{sin B}{b} = \frac{ sin C}{c}[/tex]
other methods of solving the missing sides would be using the definition of sine,cosine, and tangent
[tex]sin(\theta) = \frac{opposite}{hypothenuse}[/tex]
[tex]cos(\theta) = \frac{adjacent}{hypothenuse}[/tex]
[tex]tan(\theta) = \frac{opposite}{adjacent}[/tex]
