D is the correct answer.
I answer C with the following logic:
The 10 page that was revised twice, was revised once earlier as part of the 40 pages that was revised the first time.
Hence, (100*$5) + (40*$3) + (10*$3) = $650
Well, perhaps I think too much.
I think its D...because of the word "ONLY" - it says 40 pages were revised ONLY ONCE.....