put lessons back for Michael

docs/lessons/lucky-7/challenges.md

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+# lucky 7 blocks challenges
+
+Coding challenges for lucky 7.
+
+## Before we get started
+
+Complete the [lucky 7 activity](/lessons/lucky-7/activity) and your code will look like this:
+
+```blocks
+basic.showNumber(7)
+```
+
+### Challenge 1
+
+But we also should pause before showing another number. Let's add a pause of 500 milliseconds.
+
+```blocks
+basic.showNumber(7)
+basic.pause(500)
+```
+
+### Challenge 2
+
+What about other multiples of 7? Let's display the next multiple of 7 on the screen!
+
+```blocks
+basic.showNumber(7)
+basic.pause(500)
+basic.showNumber(14)
+```
+
+* Run the code to see if it works as expected.
+
+### Challenge 3
+
+Keep displaying multiples of 7 such as 21 and 28...
+