\(\frac{X}{sin45}=\frac{15}{sin60}\\X=\frac{15sin45}{sin60}\\X=\frac{15\times(\frac{1}{\sqrt{2}})}{\sqrt{\frac{3}{2}}}\\X=\frac{15}{\sqrt{2}}\times\frac{2}{\sqrt{3}}\\X=\frac{30}{\sqrt{6}}\\X=\frac{30}{\sqrt{6}}\times\frac{\sqrt{6}}{\sqrt{6}}=\frac{30\sqrt{6}}{6}=5\sqrt{6}\)