Short Sudoku Puzzle Translation

In this puzzle, there's a shaded box with some text (on the left) pointing to it. What does the text on the left say? Thanks for your help!

Both left and right text pointing to boxes are showing the squares you need to fill in to get some present/enter some contest.
The left one says:

全問挑戦コンテストの解答マス（詳しくはプレセントページをご覧ください)

Basically, there will be some page at the back where you can enter a contest if you fill in the right number(s) from the puzzle. Since it's the "全問挑戦コンテスト", maybe there's one from each question in the magazine or something similar.