explain why 7*11*13+13 and 7*6*5*4*3*2*1+5 are composite numbers ?

(1). 7*11*13+13 = 13(7*11+1)

= 13(77+1) = 13*78 = 13*13*2*3
Since the given number has more than 2 factors, so it is a composite number.

(2). 7*6*5*4*3*2*1+5 = 5(7*6*4*3*2+1)

= 5(1008+1) =  5 * 1009

since the given number has more than 2 factors, therefore it is a composite number