Answer:

Explanation:
We want to find the measure of ∠P. 
To do so, we can use one of the three trigonometric functions. 
Since we know the lengths of all of the sides, it doesn't matter which one we use: we will get the same result. 
Let's use the sine ratio. Recall that sine is the ratio of the opposite side to the hypotenuse. That is: 

Substitute ∠P for x. So: 

The opposite side to ∠P is 12. The hypotenuse is 13. Hence:

We can take the inverse sine of both sides: 

Use a calculator. Make sure you're in degrees mode!
So, the measure of our angle is: 

And we're done!