Answer
$525^oC$ or greater
Work Step by Step
Using $F=\dfrac{9}{5}C+32$ or the Fahrenheit conversion of Celsius, then $977^oF$ is equivalent to
\begin{array}{l}\require{cancel}
977=\dfrac{9}{5}C+32
\\\\
977-32=\dfrac{9}{5}C
\\\\
945=\dfrac{9}{5}C
\\\\
\dfrac{5}{9}\cdot945=\dfrac{5}{9}\cdot\dfrac{9}{5}C
\\\\
525=C
.\end{array}
Hence, at $\text{
$525^oC$ or greater
,}$ stibnite melts.