If the product of two roots of $x^3+k{x}^2+31x-30=0$  is 15, then $k=$

The given equation is $x^3+k{x}^2+31k-30=0$

Let the roots are $\alpha ,\beta ,\gamma$

Then product of the roots : $\alpha \beta \gamma =30$

By the given condition ,

the product of the two roots $\alpha \beta =15$

$\Rightarrow 15\gamma =30$  $\Rightarrow \gamma =2$

$\gamma =2$  is the one root of given equation

$\Rightarrow 8+4k+62-30=0$

$\Rightarrow 4k+40=0$

$\therefore k=-10$

Hence (3) is correct choice.