In the triangle with legs 7 and 9 cm, you can find the length of the hypotenuse by using the Pythagorean theorem. If the hypotenuse is [tex]x[/tex], then
[tex]7^2+9^2=x^2\implies x=\sqrt{130}[/tex]
The other right triangle with leg 6 cm and containing the angle [tex]\theta[/tex] satisfies
[tex]\sin\theta=\dfrac{6\,\rm cm}{\sqrt{130}\,\rm cm}\implies\theta=\sin^{-1}\dfrac6{\sqrt{130}}\approx31.75^\circ[/tex]
