Error 1 Operator '*' cannot be applied to operands of type 'method group' and 'double'

Question

I believe what i am trying to do is very simple but I get the error. Operator \'*\' cannot be applied to operands of type \'method group\' and \'double\'

I want to mult

Answer 1

dayrental is a function that return void.

it has no value and you cannot multiply it by 19