Here is some tips - I have gotten 6 of these so if you keep at it, you will get it within the week, you are much better at the games than I am.

The trophy is random after you get a total of 6 checkmarks on the report card. You have about a 1 in 50 chance of getting it every time you get that sixth mark. You know right away if you get the prize after you hit the last sticker to put the checkmark on.

You can get it as early as level 6 or even higher - it is possible to get more than one on a game.

You get a bonus 100 points if you use all the stickers in the level to total a sum - but only the first time you do it in the Level to get a check mark. The less numbers you use to total the sums the higher the point you are given. I try to get all three stickers on my board before a click on them. You are more likely to get the last sticker if you have the other two on the screen already.

Wait a little while when you get the apple if you are trying to get a different sticker as the apple will take away 2 sums from the total you are trying to get. I clear a row with sums before I click on the top - I bring down 4 or 6 rows and check for stickers and start using sums. I sometimes use the ones to help me clear a row (even though it is less scoring points) if I am trying for a sticker and it is near the top - especially if I am trying for a trophy.

I have gotten 6 trophies so far using this method!!