From the figure, we can conclude that the little triangle is an isosceles triangle, the greatest angle is 90 because ∠A = 90 and they are supplementary, therefore, using the triangle sum theorem:
[tex]\begin{gathered} m\angle J=m\angle K \\ m\angle K+m\angle K+90=180 \\ 2m\angle K=180-90 \\ 2m\angle K=90 \\ m\angle K=\frac{90}{2} \\ m\angle K=45 \end{gathered}[/tex]
