To solve this problem it is necessary to apply the concepts given by Malus regarding the Intensity of light.
From the law of Malus intensity can be defined as

Where
Angle From vertical of the axis of the polarizing filter
Intensity of the unpolarized light
The expression for the intensity of the light after passing through the first filter is given by

Replacing we have that


Re-arrange the equation,

Re-arrange to find \theta





The value of the angle from vertical of the axis of the second polarizing filter is equal to 30.2°
Sound level at distance of 15 m is given as 20 dB
so intensity at this distance is given as



now if we move closer to some some distance the sound level is now 50 dB
now the intensity is given as



now we know that



so now the distance from friend must be 47 cm
A. The correctly balanced equation is that in which the number of atoms of a certain element at the left-hand side is similar to that in the right hand side or the reactant side and product side, respectively. From the given equation, the answer would be,
C. Cl2 + 2NaI --> 2NaCl + I2
B. In the given chemical reaction above, heat is emitted such that it appears in the product side of the equation. Hence, this is an example of a combustion reaction.
C. Similar with the reasoning in letter A, the answer to this item is,
B. 2H2 + O2 --> 2H2O