Answer
$A \approx 58^o$
Work Step by Step
RECALL:
In a right triangle,
$\sin{A} = \dfrac{\text{length of opposite side}}{\text{length of hypotenuse}}$
$\cos{A} = \dfrac{\text{length of adjacent side}}{\text{length of hypotenuse}}$
$\tan{A} = \dfrac{\text{length of opposite side}}{\text{length of adjacent side}}$
Use the sine formula above to obtain:
$\sin{A} = \dfrac{17}{20}$
Use the inverse sine function to obtain:
$A = \sin^{-1}{(\frac{17}{20})}
\\A = 58.21166938^o
\\A \approx 58^o$