7 + 3 x 14 + 6 x 7^2 + 6 x 7^3 + 6 x 7^4 + 6 x 7^5 + 6 x 7^6 + 6 x 7^7 =  Choose the most appropriate option:  A) 7^21  B) 7^14  C) 7^10  D) 7^8  E) None of the above
Let's see that 7 + 3 x 14 is 49 or 7^2, then: 7^2 + 6 x 7^2 becomes 7 x 7^2 that is 7^3. So we follow with the next element: 7^3 + 6 x 7^3 is equal to 7 x 7^3 that is 7^4. Then is assumed right before 6 x 7^7: 7^7 + 6 x 7^7 becomes 7 x 7^7 that is 7^8. Thus, the correct answer is the option 7^8, 7^8.
<result>D</result>
7 + 3 x 14 + 6 x 7^2 + 6 x 7^3 + 6 x 7^4 + 6 x 7^5 + 6 x 7^6 + 6 x 7^7 =