\[7x^{2} - 5x + 3 + 7x^{2} - 5 =\]
\[= 14x^{2} - 5x - 2.\]
\[7x^{2} - 5x + 3 - \left( 7x^{2} - 5 \right) =\]
\[= 7x^{2} - 5x + 3 - 7x^{2} + 5 =\]
\[= - 5x + 8.\]