#### Answer

$120^0$

#### Work Step by Step

From the law of cosines
$7^{2}=3^{2}+5^{2}-2\times 3\times 5\times \cos \theta \Rightarrow 49=34-30\times \cos \theta \Rightarrow -30\cos \theta =15\Rightarrow \cos \theta =-\dfrac {1}{2}\Rightarrow \theta =\cos ^{-1}\left( -\dfrac {1}{2}\right) =120^0$