Question

describe why 7.11.13+13 and 7.6.5.4.3.2.1+5 are composite numbers

Answer 1

7×11×13+13,

13(7×11+1),

13×78,

since 13×78 have more than two factors then it will be a composite number.
because 13×78 is exactly divisible by 1, 13, 2, 78 and much more number then it's a composite number....

composite number:- A number having more than two factors is known as composite number.



And same approach for the next part.....