The trinomial $\displaystyle{7}{{x}}^{{2}}+{17}{x}+{6}\usepackage{cmbright}\Huge\$ has been factored below, but the two constants have been left out.

$\displaystyle{7}{{x}}^{{2}}+{17}{x}+{6}={\left({7}{x}+{a}\right)}{\left({x}+{b}\right)}\usepackage{cmbright}\Huge\$

What is the value of the constant a?