30g of hot water at 80°c is mixed with 50g of cold water at 25°c. calculate the final temperature

B, if it was a lower watt she could put it in for her normal time and not burn it

Velocity is the speed of an object in a certain direction so you'd need to know speed and direction

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current

If your workout exceeds an hour you should substitute "a sports drink" for water.hope my answer has you : )