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.