Let 'a', 'b', 'c' and 'd' be the prime number in ascending order. The product of the first three is 7429 and last three is 12673. Find the first number.

Given that $$a*b*c =  7429$$ and $$b*c*d =  12673$$

Therefore, $$\dfrac{b*c*d}{a*b*c} = \dfrac{12673}{7429}$$ 

$$\Rightarrow$$ $$\dfrac{d}{a} = \dfrac{29}{17}$$

Since a and d are prime number there won't be any common factor which can divide both. Hence, a = 17, b = 19, c = 23 and d = 29. 

Therefore, option B is the correct answer.