An echo is heard on a day when temperature is about 22°C. Will echo be heard sooner or later, if the temperature increases to 40°C?
Echo will be heard sooner than the echo heard when temperature was 22°C.
Because speed of sound increases with increase in temperature.
Also, speed or sound in air =Distance/time
i.e. If speed of sound increases, then time after which the echo will be heard decreases.