Since this is a right triangle, we can use one of the three main trigonometric functions: sine, cosine, or tangent.
Remember: SOH-CAH-TOA
Looking from angle I, we know the opposite side and the hypotenuse. Therefore, we should use sine.
sin(I) =
To solve, you can use your calculator and the inverse sine function (sin^-1).
I = sin^-1()
I = 61 degrees
Hope this helps!