At 1:00 pm, there were 10.0 grams of bacteria. The bacteria increased to x grams at 4:00 pm, and 16.9 grams at 7:00 pm. If the amount of bacteria present increased by the same fraction during each of the 3-hour periods, how many grams of bacteria were present at 4:00 pm?	Pick one:
A) 13.0
B) 13.3
C) 13.6
D) 13.9
E) 14.2

Rationale: "let x be the factor by which the bacteria increases every three hours . at 4 : 00 pm , the amount of bacteria was 10 x and at 7 : 00 pm it was 10 x ^ 2 . 10 x ^ 2 = 16.9 x ^ 2 = 1.69 x = 1.3 at 4 : 00 pm , the amount of bacteria was 10 ( 1.3 ) = 13 grams . the answer is a ."
Answer: A