Watch closely. I'll try to go slow:
You said <u>v² = 2 g t</u>
Divide each side by 2g : <em>v² / 2g = t</em>
Did you follow that ?
Radian: is the standard unit of angular measure, used in many areas of mathmatics.
degree: is a measuement of plane angle, defined by representing a full rotation as 360 degrees.
Both are two units for measuring angles. There are at least four such units, but degrees and radians are most likely to encounter high school and college.