You have a box which contains only red marbles and blue marbles. The mass of one red marble is 16 grams, while the mass of one blue marble is 20 grams. If the box contains 21 red marbles and 18 blue marbles, what is the total mass of the marbles in the box?

Answer 1

that would be 21*16 + 18*20 = 696g

Answer 2

the mass of one red marble is 16g and you have 21 red marbles, therefore
16.21=336grams
And you have 18 blue marbles and the mass of one blue marble is 20 grams
therefore, 20.18=360g
336g+360g=696grams total in the box..
I hope my answer is correct.