Answer:
The angle measures approximately 18.19°. 
Explanation:
Since we want to find the angle and we are given the side adjacent to the angle and the hypotenuse, we can use the cosine ratio. Recall that: 

The adjacent side is 19 and the hypotenuse is 20. Substitute: 

We can take the inverse cosine of both sides: 

Use a calculator (make sure you're in Degrees Mode!). Hence: 

The angle measures approximately 18.19°.