I did this by looking at the bottom line and realising that the central triangle touched halfway, so I drew a vertical line from this point upwards. This then shows that the triangle on the right is half of the rectangle you have just created, therefore the triangle is 1/4 of the entire square. on the left hand side the central triangle's point touches halfway too and I drew the line horizontally across; now the square is in quarters. the top 2 quarters are split in half by a second triangle which makes that triangle a quarter and together with the triangle on the right a half. Half of one of the smaller squares ( bottom left ) is filled with a tiny right-angled triangle, and half a quarter is an eighth so the small triangle is one-eighth of the entire square. So now you have one-eighth and a half which makes 5/8. 8 minus 5 equals 3 so the central triangle is three as that is the remaining value!
So this is the answer:
Bottom left triangle = 1/8
Top triangle = 2/8
Triangle to the right = 2/8
Central triangle = 3/8