Question 260088
n*(n+1)=n+n+1+71
n^2+n=2n+72
n^2-n-72=0-
(n-9)(n+8)=0
n=9 (and 10) and n= -8 (and  -7)

check
9*10=19+71
90=90
-8*-7=-8-8+1+71
56=72-16
56=56