imc

Let $a$ be the amount of triangular tiles and $b$ be the amount of square tiles. Triangles have $3$ edges and squares have $4$ edges, so we have a system of equations. We have $a+b$ tiles total, so $a+b=25$. We have $3a+4b$ edges total, so $3a+4b=84$. Multiplying the first equation by $3$ on both sides gives $3a+3b=3(25)=75$. Second equation minus the first equation gives $b=9$, so the answer is $\boxed{9}$.