To prove the divisibility lets expand each number first to get the complete picture of the problem
51^7 = 8.974106779 . 10^11
51^6 = 1.75962878 . 10^10
(51^7 - 51^6) = 8.974106779 . 10^11 - 1.75962878 . 10^10
= 8.798143901. 10^11

= 3.51925756. 10^10
That is the answer expressed in scientific notation
= 35192575600
Which means the divisibility is proven
Yes. In fact
is a Pythagorean triple or simply right triangle where all sides are in
.
Hope this helps.
The answer is 240 :3
60+60= 120
120+60 = 180
and 60 more would be 240
60 fours would be 240
3 60's would be 180. So your answer is 240