Answer:
it is 27 degree.
Explanation:
because angle of reflection is equal to angle of Inc dence
To solve this problem we will apply the concepts related to the calculation of the speed of sound, the calculation of the Mach number and finally the calculation of the temperature at the front stagnation point. We will calculate the speed in international units as well as the temperature. With these values we will calculate the speed of the sound and the number of Mach. Finally we will calculate the temperature at the front stagnation point.
The altitude is,

And the velocity can be written as,


From the properties of standard atmosphere at altitude z = 20km temperature is



Velocity of sound at this altitude is



Then the Mach number



So front stagnation temperature



Therefore the temperature at its front stagnation point is 689.87K
The Answer Is : D. 20.0 cm
My Reason : These types of problems can all be solved using the lens or mirror equation.
1/20 +1/q= 1/10
q=20 cm
The image is formed behind the lens at 2f or the center of curvature.
It is real, inverted, and the same size as the object
Gravity!! It also keeps the planets in orbit!