I think you almost got it.
At the top, the velocity only has horizontal component, so v=12 m/s is v_x, which is v*cos(theta), because v_x is constant, so the same when it was launched or now.
With the value of the initial speed (28 m/s, which is the total speed), you can set
v_x = v * cos( theta ) ---> 12 = 28*cos(theta) --> cos(theta)=12/28=3/7
or theta = 64.62 deg, it is D. Think about it. I hope you see it.
The electrostatic force is directly proportional to the product of the charges, by Coulomb's law.
F α Qq
If the charges are now half the initial charges:
<span>F α (1/2)Q *(1/2)q
</span>
F α (1/4)Q<span>q
The new force when the charges are each halved is (1/4) the first initial force experienced at full charge.</span>
First convert the speed of sound from meters/second to miles/second:

Then the time it takes for the sound to travel 20 miles is

at t=T/6, total distance covered= 2*pi*r/6 and displacement= r
difference of them = 2*t
so, 2*pi*r/6- r =2(1/6)=1/3
r=1/(pi-3)=7.062