[tex]\bf \pm \sqrt{7^2-(2\sqrt{10})^2}=b\implies \pm\sqrt{49-(2^2\sqrt{10^2})}=b
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\pm\sqrt{49-(4\cdot 10)}=b\implies \pm\sqrt{9}=b\implies \pm 3=b
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\textit{no quadrant is given for the angle, so, we can just assume is the +3}
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sin(\theta)=\cfrac{opposite}{hypotenuse}\qquad \qquad sin(\theta )=\cfrac{3}{7}[/tex]