1) Build a table for the function
T velocity = 20√(273 + T)
°C m/s
-3,00 328,63
-2,50 328,94
-2,00 329,24
-1,50 329,55
-1,00 329,85
-0,50 330,15
0,00 330,45
2) The graph is attached. In it the value at which the velocity is 329 m/s is very close to the y-axis, so x is close to zero (negative).
3) Conclusion: You can see that the value of temperature (T) for which the velocity is 329 m/s is -2,50 °C