Based on the data provided, we can see that the mass of a gerbil at birth is 2 grams and at 4 weeks old is 50 grams. The mass appears to be increasing at a fairly consistent rate. If we assume that the trend continues, a good approximation of a gerbil's mass at exactly 5 weeks old would be between 200 grams and 250 grams. Therefore, the best option would be 3. 250 grams.
