Answer: 4 boxes of baseballs weigh 120 pounds and 400 boxes weigh 12,000 pounds.
Explanation:
We know that 40 boxes of baseballs weigh a total of 1,200 pounds.
So we can just that the unit rate of this by doing 1,200/40 = 30
After that we get that 1 box of baseballs weigh 30 pounds.
Next to find out how much 4 boxes of baseballs weigh we do 30 * 4 = 120 pound.
Lastly to find out how much 400 boxes of baseballs weigh we do 30 * 400 = 12,000 pounds