The smaller triangle to the upper right, with sides [tex]y[/tex], 36 and 60, is similar to the larger triangle whose hypotenuse is [tex]x[/tex]. The corresponding angle [tex]\theta[/tex] is labeled in the attached image. It satisfies
[tex]\sin\theta=\dfrac{36}{60}=\dfrac{60}x[/tex]
which tells you that
[tex]\dfrac{36}{60}=\dfrac{60}x\implies x=\dfrac{60^2}{36}=100[/tex]
