\[\frac{x^{2}}{x^{2} + 2x + 1} - \frac{3x - 4}{3x + 3} =\]
\[= \frac{x^{2}}{(x + 1)^{2}} - \frac{3x - 4}{3 \cdot (x + 1)} =\]
\[= \frac{3x^{2} - (3x - 4)(x + 1)}{3 \cdot (x + 1)^{2}} =\]
\[= \frac{x - 4}{3 \cdot (x + 1)^{2}} = \frac{19 - 4}{3 \cdot (19 + 1)^{2}} =\]