Pokedummy - Above the 25 line it is easily logical, no temporaries needed. Below the 25 line, use temporaries for the 7s. e.g. Place the left-most 7 as far left as possible and see what happens. If it works, great! If not, then the left-most square cannot be part of that 7 and must be blank.
This is a 4-star difficulty rating. If it's too hard, work on 2- and 3-star difficulty puzzles until you develop your skills. That's what I did, and now I can even tackle some of the 5-star difficulties! :)