Which formula can be used to solve problems related to the first law of thermodynamics?

Q = ΔU + W
Q is the exchanged heat.
ΔU is the total change in the internal energy of a system.
W  is the work done by or on the system.
The statement of the First Law is Thermodynamics is: “energy can be converted from one form to another with the interaction of heat, work and internal energy, but it cannot be created nor destroyed, under any circumstances”.

the answer is a. at the equator

grav force prop 1/r squared 2r all squared is 4rsquared 1/4rsquared quartered