Displaying both numeric and text values in Label using Arcade?

I am using ArcGIS Online.

I had created this label using Arcade because I had to customize the wind speed outcome from km/h to mph. I wanted to add "mph" to label after the wind speed value, but am not having any luck with the Text function in Arcade.

Can someone help me with this task?

$feature.WIND_SPEED / 1.6;