Its is a convex!!
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By convention angles are measured from the normal to the reflecting surface. The angle of incidence, 35 degrees, is equal to the angle of reflection. In this case 35 degrees. The answer is 35 degrees.
A convex reflector.
a tangent
The reflecting surface must be sufficiently smooth and shaped such that the sound is reflect back and not dispersed. Sound travels at approx 340 metres per second and the average human brain easily can distinguish sounds that are 1/2 second apart. That means the sound must travel at least 170 metres so that the reflecting surface must be half that distance away. While a greater distance will create a more distinctive echo, the strength of the returning sound fall off rapidly (at twice the square of the distance to the reflecting surface). In normal circumstances 170 metres (= approx 500 feet) is a good distance. A cave or convex reflecting surface will allow a greater distance.
Any smooth surface will reflect light. The better question is "How much light does each kind of smooth surface reflect?"