Puzzle 1 - How many triangles? (see below for entry details)

How Many Triangles?

Beginning 6th March, a weekly maths puzzle competition will be set for students every Monday morning (notice board outside R330). All students are welcome to submit answers by Friday of each week (submission folder on notice board). Every Friday, a student will be selected at random from the correct answers and will receive a small prize. Submitted answers must have student's name and class. Puzzles that require solution workings must have those workings included on the answer sheet. Won't be as easy as it sounds. You can count on it...Good luck!