Ans is 6 yellow triangles.

1 red sq. = 1 blue circle + 1 yellow triangle

Multiply whole eq. With 2 we get;

2 red sq. = 2 blue circle + 2 yellow triangle. .... (A)

From 2nd image;

1 blue circle = 2 yellow triangles

Using this in equation (A), we get;

2 red sq. = 2 + 2 yellow triangles + 2 triangle s

2 red sq. = 6 yellow triangles.