Question 1104065
.
The plot below is your HINT.


Two roots are x= 3  and  x= 0.5.


<pre>
{{{graph( 330, 330, -3.5, 5.5, -20.5, 5.5,
          2*x^4-3*x^3-7*x^2-8*x+6
)}}}


Plot y = {{{2*x^4-3*x^3-7*x^2-8*x+6}}}
</pre>

Can you do the rest ?