Concept: The question is a conversion problem

Solution:

Given,1 cubic meter = 1,000,000 cubic centimeters

= 7.3 x 1,000,000 grams (1 cubic centimeter of a certain substance is 7.3 grams,(given))

= 7.3 x 1000 kg (1kg=1000 grams given)

=7300 kg (OPTION D)