A right triangle can be drawn to model the geometry of the problem. The hypotenuse of the triangle is the length of the string, 100 ft. The side opposite the angle is the height of the kite above the ground, 85 ft.
The mnemonic SOH CAH TOA reminds you of the relationship between sides and angles.
Sin = Opposite/Hypotenuse
sin(α) = (85 ft)/(100 ft) = 0.85
The angle whose sine is 0.85 is found using the arcsine (inverse sine) function:
α = arcsin(0.85) ≈ 58.2°
The angle of elevation is about 58°.
_____
When using your calculator to find the values of inverse trig functions, make sure it is in <em>degrees</em> mode. Otherwise, you're likely to get the answer in radians (≈ 1.01599 radians).