Question

Please help me with this problem

Answer 1

Put 5 where n is in the formula and do the arithmetic. I find it convenient to rewrite the formula to make evaluation simpler.

`a_n=((n+1)n-9)n-9\\\\a_5=((5+1)5-9)5-9=21\cdot 5-9=\bf{96}`

... matches the 2nd choice