Step-by-step explanation:
Given that;
In a 60 minute boxing class Abby burns 480 calories.
The rate at which calories are burn during boxing is;

Also;
on a 40 minute run,Abby burns 440 calories,
The rate at which calories are burn during cycling is;

while cycling for 30 minutes,
From the above rate the most efficient exercise at burning calories is the exercise with the highest rate of burning calories.