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)