Question

(0,0), (1,5), (2,20), (3,45), (4,80) what's the rule?

Answer 1

Hmm, seems to multiply by 5
wait, no

first is multiply by 5
2nd is multiply by 10
3rd is multiply by 15
4th is multiply by 20
seems to be

$f(x)=x(5x)$ or $f(x)=5x^2$
the rule is square the input then multiply by 5