Hi!
To solve this, I would use tan, as tan is opposite / adjacent. In this case, the opposite is 20, and the adjacent is 21. You would use the fraction 20/21, to find the measure of angle I.
As the function tan() is finding the ratio of the sides from a degree, but we already know the ratio of the sides and are looking to find the degree, then instead we'll be using the function [tex] tan^{-1} () [/tex].
If you put the fraction 20/21 into that function, you get [tex] tan^{-1} (20/21) [/tex]. And if you solve that with a calculator, you get your answer of roughly 43.6. So your answer is the third option, or 43.6 degrees.
Hope this helped!
