Explanation

SOLUTION $$\begin{gathered} \sqrt{12}-\sqrt{147}+y\sqrt{3}=0 \\ \sqrt{4\times 3}-\sqrt{49\times 3}+y\sqrt{3}=0 \\ 2\sqrt{3}-7\sqrt{3}+y\sqrt{3}=0 \\ y\sqrt{3}=7\sqrt{3}-2\sqrt{3} \\ y=\frac{5\sqrt{3}}{\sqrt{3}} \\ y=5 \end{gathered}$$

SOLUTION $$\begin{gathered} \sqrt{12}-\sqrt{147}+y\sqrt{3}=0 \\ \sqrt{4\times 3}-\sqrt{49\times 3}+y\sqrt{3}=0 \\ 2\sqrt{3}-7\sqrt{3}+y\sqrt{3}=0 \\ y\sqrt{3}=7\sqrt{3}-2\sqrt{3} \\ y=\frac{5\sqrt{3}}{\sqrt{3}} \\ y=5 \end{gathered}$$