A star is written to show multiplication. It is a replacement for a dot or a x which is what you probably learned to be the "times" sign. In upper level maths, the "x" is replaced with a " * " to make it more legible and to avoid confusion with the variable "x".
The answer is 1 day because if it takes Doug 3 days by himself and if his son helps him and it takes 2 days with the both of them that means it would only take Doug's son 1 day.
