Explanation:

- The problem mentions twelve numbers with an average of 46. Therefore, their total sum is $12\times 46=552$.

- The first four numbers have an average of 43, giving a total sum of $4\times 43=172$.

- The last five numbers average 49.4, giving a total sum of $5\times 49.4=247$.

- Now, subtract the sum of the first four and the last five numbers from the total sum: $552-172-247=133$. This is the sum of the 5th, 6th, and 7th numbers.

- Let's say the 7th number is $x$. Then, the 5th number is $x+4$ and the 6th number is $x+6$.

- Their sum $(x)+(x+4)+(x+6)=3x+10=133$. Thus, $3x=123$ and $x=41$.

- The 5th number is $41+4=45$.

- The average of the 5th and 7th numbers is $(45+41)/2=86/2=43$.

Option 2: 43 is the correct answer.