Answer: 6.7
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Explanation:
Draw out a right triangle as you see below.
Let's use the pythagorean theorem to find 'a'
[tex]a^2 + b^2 = c^2\\\\a = \sqrt{c^2 - b^2}\\\\a = \sqrt{(9.9)^2 - (7.3)^2}\\\\a = \sqrt{44.72}\\\\a \approx 6.6873\\\\a \approx 6.7\\\\[/tex]
