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28 shaded triangles

Step-by-step explanation:

First, we have 0 shaded triangles.

Then we have 1 shaded triangle

then we have 3 shaded triangles

then we have 6 shaded triangles

In each new triangle, we add a base with a larger number of triangles.

In the base of the fourth triangle we have 3 triangles, then in the next triangle we have a base of 4 triangles, then we have 4 + 3 + 2 +1 triangles = 10 triangles.

in the sixth triangle the base has 5, so here we have 5 + 4+ 3 + 2 +1 = 15 triangles

in the seventh the base has 6 triangles, so here we have 15 + 6 = 21 shaded triangles

and in the height triangle, the base has 7 triangles, then we have 28 shaded triangles

2.56 is the width of the garden

step-by-step explanation: