Question

a quantity has a value of -6.0 m/s . it may be

Answer 1

Heya

∆ Velocity is a Vector Quantity

=> Along with a certain magnitude, and the S.I. unit of course, the +ve or the -ve sign indicates its linear direction, i.e., whether it's moving in a relatively +ve direction or a -ve direction

Concerning it's Dimensional Formula :
$( {m}^{0 } {l}^{1} {t}^{ - 1} )$

-> It is the magnitude of Velocity of an object going in a -ve direction 180°