Why is the loss of mass of the object only an apparent loss?

when jerome paddle in flowing river towards east the net speed of jerome will increase

so the net speed of jerome will be given as

now the speed of paul will be same as it is given as he is running on the ground

so

so here we can say since the speed of jerome is more so he will win the race

now as we know the distance so the time difference is given as

so jerome will reach first and the time difference will be 203.55 s or 3.4 min

if i am correct, your answer choices are:

a. the temperature remains constant

b. the temperature increases at a constant rate

c. heat flows at a constant rate into the system

d. heat flows at a constant rate out of the system

e. no heat flows into or out of the system

if so, then the answer is e. no heat flows into or out of the system.