I have:
$$T(x) = -\frac1{10}x^2 + \frac{24}{10}x - \frac{44}{10}$$
$T$ = temperature
$x$ = hour
And they ask me to find the hour in which the temperature reached zero. So I know I must replace:
$$0 = -\frac1{10}x^2 + \frac{24}{10}x - \frac{44}{10}$$
It's very easy, I know, but I really don't remember how to clear/free the $x$ in this case.