Answer:The length of the second box is 40 units.
Explanation;We have to first find the volume of the second box by writing side x side x side the we substitute in by writing 10 units x 10 units x 10 units the answer we get will be 1000 units. After all that to find the length of the second box since the question says that the rectangular box has twice the volume of the square box we have to double the volume of the square box which is 1000 units x 2=2000 units. After getting the volume of the second box to find the length we shall have to write length x width x height=volume then we write L x 10 x 5 units=2000 cubic units then L x 10 units x 5 units/10 units x 5 units=2000 units x units x units/10 units x 5 units we then cancel 10 units by by 10 units and 5 units by 5 units and remain with L=40 UNITS.