First you'll need 18 turtles. You already have one, so hatch 17 more.
If you lose track, you can easily find the number of the last turtle hatched. Check. Now change the shape of every turtle to a sun. Check.
Drag each turtle to its final position - they can be just scattered about if you prefer - the important thing is to freeze each one. Check.

Each turtle will need a "hidden" shape so let's give each turtle a new property called hidden_shape. Check.

The 18 shapes will consist of nine pairs - so we need a list of nine different shapes. Check. Two lists can be combined together using the turtle word sentence. For example, show sentence [Mary had a] [little lamb] Can you build the shapes box up to 18 members using this magic new word? Check.

How can we pick out an item from this list? By using the new turtle word item which works like this show item 7 :shapes - try it yourself. Assign this 7th item to the hidden_shape property of the 7th turtle. Check.

So you could write 18 lines to assign the 18 shapes and that will work fine. However, try to do it using everyone and a memory box as a counter. Call your procedure start. Check.