If tan (3x + 30°) = 1 then x = ?

As we know that,

$\tan 45^{\circ}=1$

Thus,

if $\tan \left(3 x+30^{\circ}\right)=1$

$\Rightarrow 3 x+30^{\circ}=45^{\circ}$

$\Rightarrow 3 x=45^{\circ}-30^{\circ}$

$\Rightarrow 3 x=15^{\circ}$

$\Rightarrow x=5^{\circ}$

Hence, the correct option is (d).