с переводом выражения
What is their secret? Metal buckets, perhaps.
Речь идёт о людях, которые много едят , но не поправляются. Может это какая-то идиома? Не могу ничего найти в интернете

they will have planted trees in their garden by 7 o'clock tomorrow в future in the past будетиметьтакойвид: they would have planted trees in their garden by 7 o'clock tomorrow. соответственно вопросы будут следующие:

would  they have planted trees in their garden by 7 o'clock tomorrow?

would  they have planted trees or flowers in their garden by 7 o'clock tomorrow?

who would  have planted trees in their garden by 7 o'clock tomorrow?

what would  they have planted in their garden by 7 o'clock tomorrow?

where would  they have planted trees by 7 o'clock tomorrow?

when would  they have planted trees in their garden?

what would  they have done in their garden by 7 o'clock tomorrow?

they would have planted trees in their garden by 7 o'clock tomorrow, wouldn’t they?  

if you have a best friend you can always rely on him. if you have trouble, he will always be there and always help.