Answer
$2 \sqrt 3$
Work Step by Step
Given expression
= 4 $\cos( z - 30^{\circ})$
= 4 $\cos(60^{\circ} - 30^{\circ})$
( replacing z with $60^{\circ}$)
= 4 $\cos 30^{\circ}$
= 4 $\times (\frac{\sqrt 3}{2})$
( substituting for exact value of $\cos 30^{\circ}$)
= $2 \sqrt 3$
