$7{x}^{2}+x-21x-3$
Factor out $x$ from the expression$x \times \left( 7x+1 \right)-21x-3$
Factor out $-3$ from the expression$x \times \left( 7x+1 \right)-3\left( 7x+1 \right)$
Factor out $7x+1$ from the expression$\left( 7x+1 \right) \times \left( x-3 \right)$