Answer:
Step-by-step explanation:
If all were 30-pound boxes, the total weight would be 30ยท125 = 3750 pounds. The actual weight is 5700-3750 = 1950 pounds more than that. Each 60-pound box that replaces a 30-pound box increases the weight by 30 pounds, so there must have been 1950/30 = 65 such replacements.
The truck is carrying 65 60-pound boxes and 60 30-pound boxes.