The pK _ b of dimethylamine and pK _ a of acetic acid are 3 . 27...

${pk}_{b}$ of dimethylamine $= 3 . 27$
${pk}_{a}$ of acetic acid $= 4 . 77$

Dimethylammonium acetate is salt of weak acid and weak base for which $pH$ is:

$pH = 7 + \dfrac{1}{2}{pk}_{a} - \dfrac{1}{2}{pK}_{b}$

$= 7 + \dfrac{1}{2} \times 4 . 77 - \dfrac{1}{2} \times 3 . 27$

$= 7 . 75$