In the diagram, each scale shows the total mass (weight) of the shapes on that scale. What is the mass (weight) of a $\triangle$ ?
(A) 3
(B) 5
(C) 12
(D) 6
(E) 5.5

![](https://cdn.mathpix.com/cropped/2024_04_20_46ead6524a8d61e21c51g-069.jpg?height=136&width=613&top_left_y=1309&top_left_x=1076)
The first scale tells us that a square and a circle together have a mass of 8 .

The second scale tells us that a square and two circles together have a mass of 11.

We can replace the square and one circle on the second scale with an " 8 ", so 8 plus the mass of a circle gives a mass of 11 . This tells us that the mass of a circle is 3 .

From the third scale, since the mass of a circle and two triangles is 15 , then the mass of the two triangles only is $15-3=12$.

Therefore, the mass of one triangle is $12 \div 2=6$.

ANSWER: (D)