I need help with #3. Please help. I have to show all work so please explain

Answer:
a = 2
Step-by-step explanation:
Use Pythagorean Theorem:
[tex]a^2+b^2=c^2\\a^2+2.1^2=2.9^2\\a^2+4.41=8.41\\a^2=4\\\sqrt{a^2}=\sqrt{4}\\a=2[/tex]
Therefore, a is 2 meters.