Answer:
[tex] {y} = 6\sqrt{3} \:units [/tex]
Step-by-step explanation:
By Pythagoras Theorem:
[tex] {y}^{2} = {(9 + 3)}^{2} - {(6)}^{2} \\ \\ {y}^{2} = {(12)}^{2} - {(6)}^{2} \\ \\ {y}^{2} = 144 - 36 \\ \\ {y}^{2} = 108 \\ \\ {y} = \sqrt{108} \\ \\ {y} = \sqrt{36 \times 3} \\ \\ {y} = \sqrt{ {6}^{2} \times 3} \\ \\ {y} = 6\sqrt{3}\:units [/tex]
