jmc

Replace a triangle with the letter $a$ and a circle with the letter $b.$ The two given equations become $$\begin{array}{rl}3a+2b& =21\\ 2a+3b& =19.\end{array}$$Multiplying the first equation by $2,$ we get $6a+4b=42.$ Multiplying the second equation by $3,$ we get $6a+9b=57.$ Subtracting these two equations to eliminate $a,$ we have $5b=15.$ Multiplying both sides by $\frac{3}{5},$ we get $$\frac{3}{5}\cdot 5b=\frac{3}{5}\cdot 15\Rightarrow 3b=9.$$Thus, three circles equals $\boxed{9}.$