Distance , d = a+b[tex]t^2[/tex]
The unit of d is in meter and t is in seconds.
So the unit of a a must be meter.
Now we have unit of b[tex]t^2[/tex] is meter.
So unit of b*[tex]second^2[/tex] = meter
Unit of b = meter/[tex]second^2[/tex]
So unit of a = m and unit of b = m/[tex]s^2[/tex].