Background:
So with sine cosine and tangent, try remembering the following:
Sin : Opposite / Hypotenuse
Cos: Adjacent / Hypotenuse
Tan: Opposite / Adjacent
Or just remember "Soh-cah-toa".
Thinking Process:
Anyways, with this, its asking for the sine ratio of angle Z. So we need the opposite side length and the hypotenuse side length
For the opposite side length, look to see where the angle is "opening" up towards, like a door that is opening. With this, Angle Z is opening up towards the Side XY, which has a length of 21.
To find the hypotenuse, it is always the largest side length of a right triangle. It is also where the right angle opens up it's "door" up to. This would be Side XZ, which has a length of 29.
Answer:
With both of these, back to the ratio formula:
Sin : Opposite / Hypotenuse
To finish the question, simply plug in the values that were found above.
This will give you:
Sin Z : 21 / 29
This will be Choice A.