Where is a good place to start?
Have you looked at some of the examples on the sheet?
How many different triangles do you think you can draw with the
lengths of the two perpendicular and horizontal sides making any
total up to $15$? Can you list some? How do you know you can list
them all without missing any out?
Have you thought of trying the "family" of triangles with a height
of one?
Do you need to draw all the triangles in a family to see if any
meet the requirements? How can you tell?
You have pitched your tent (the red triangle) on an island. Can you
move it to the position shown by the purple triangle making sure
you obey the rules?