To boil methane, you must add 760 kJ of heat per kilogram of methane. If you boil 1 kg of methane, the entropy increases by 6.72 KJ/K. What is the temperature at which methane boils
(in Celsius)?

wavelength divides in half and speed stays the same.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.

electrical potential energy =0.072 j

explanation:

electrical potential energy is given by

u= q δv

q= charge=6 c

δv= potential difference and is given by

δv= e d

e= electric field

d= distance=5 mm=0.005 m

δv=2.4 (0.005)=0.012 v

now electric potential energy= u= q δv

u=6 (0.012)

u=0.072 j