HELP?!!!

Dust of Snow by Robert Frost
The way a crow
Shook down on me
The dust of snow
From a hemlock tree
Has given my heart
A change of mood
And saved some part
Of a day I had rued.

Justify the length of the final line in relation to all the others. (Hint: consider why Frost used “had rued” instead of the simple past “rued”.)

Is this your homework?

^ You counted them incorrectly.

Tis 4-4-4-5-5-4-4-6

I did Robert Frost last year, this was one of my fave poems in the anthology but i never did my CW on this one. I think its something to do with effect
*Gem*

I think it gives the poem a unique... twist, of sorts, having some of the lines different from others. I do that sometimes, accidentally.