To find the angle \( x \) in the right triangle where the side lengths are given as 21 (hypotenuse) and 15, we can use the sine function.
In a right triangle, the sine of an angle is defined as the ratio of the length of the opposite side to the length of the hypotenuse. Here the opposite side to angle \( x \) is 15, and the hypotenuse is 21.
Using the sine function: \[ \sin(x) = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{15}{21} \]
Now simplify \( \frac{15}{21} \): \[ \frac{15}{21} = \frac{5}{7} \]
Now take the inverse sine (arcsin) to find angle \( x \): \[ x = \arcsin\left(\frac{5}{7}\right) \]
Using a calculator: \[ x \approx 44.43° \]
Rounding to the nearest degree gives: \[ x \approx 44° \]
Therefore, the answer is \( 44° \).