We are given three units as to the possible numbers hiding behind the figures, and the easiest one to work with is CLUE 2.
This says the triangle must be 8.
Now let us turn to others which are a little tricky.
Clue 1 says
triangle + diamond + star = 22
Clue 3 says
star - diamond = traingle
clue 4 says
2 + diamond + diamond = triangle
From clue 4 we see that since triangle = 8, we have
2 + diamond + diamond = 8
subtracting 2 from both sides gives
diamond + diamond = 6
meaning diamond = 6
From clue 1 putting in the values of the diamond and the triangle we get
star = 11.