Answer
$\frac{7}{2}=3.5, \ or, \ -3$
Work Step by Step
For the equation $10x^2 -5x-105 = 0$, we use the quadratic formula as follows
$$
x=\frac{-b \pm \sqrt{b^{2}-4 a c}}{2 a},
\\
a=10, \quad b=-5, \quad c=-105
.$$
That is, $$ x=\frac{5 \pm \sqrt{25+4(10)(105)}}{20 }=\frac{7}{2}=3.5, \ or, \ -3
.$$
