I'm trying to add a number of days (actually a number of weeks) to an existing date in Go. I have tried 
`myDate.Add(time.Hour * 24 * 7 * weeksToAdd)`

But I get an error when I try to build: `invalid operation: time.Hour * startAdd (mismatched types time.Duration and float64)`

So `weeksToAdd` is currently a `float64`, but I can change it to an int or whatever. Changing it to an int only changed my error to say that `int` and `Duration` can't be multiplied.

How do I add days to a date?