Lessons 15,17-19 updated

3 lat temu · 23214bdd30
--- a/Lesson15/Lesson15.odp
+++ b/Lesson15/Lesson15.odp
--- a/Lesson15/Lesson15.pdf
+++ b/Lesson15/Lesson15.pdf
--- a/Lesson17/Lesson17.odp
+++ b/Lesson17/Lesson17.odp
--- a/Lesson17/Lesson17.pdf
+++ b/Lesson17/Lesson17.pdf
--- a/Lesson18/Lesson18.odp
+++ b/Lesson18/Lesson18.odp
--- a/Lesson18/Lesson18.pdf
+++ b/Lesson18/Lesson18.pdf
--- a/Lesson19/Lesson19.odp
+++ b/Lesson19/Lesson19.odp
--- a/Lesson19/Lesson19.pdf
+++ b/Lesson19/Lesson19.pdf