Alexandra decides to climb mt. krumpett, which is 5000 m high. she determines that this will require a total of 1350 kcal of energy for the trip. for her food supply, she decides to take nutrition bars. the label states that each bar contains 50 g of carbohydrates, 10 g of fat, and 40 g of protein. how many nutrition bars does alexandra need to take with her?

Alexandra requires a total energy of 1350 kcal for the climb
by eating proteins, fats and carbohydrates the amount of calories per gram contributed varies.
Proteins and carbohydrates - 4 calories per gram 
fats - 9 calories and gram
This means that by eating the same mass of fats and proteins/ carbohydrats the calories gained from fats is higher.
each bar contains;
50 g of carbohydrates - 4 calories/g x 50 g = 200 calories
10 g of fat - 9 calories/g x 10 g = 90 calories 
40 g of protein - 4 calories/g x 40 g = 160 calories 
total amount of calories from 1 bar = 200 + 90 + 160 = 450 calories 
energy required = 1 350 000 calories 
bars required = 1 350 000/450 = 3000
alexandra should consume 3000 bars 

The answer is solid copper