Step-by-step explanation:
speed is given by the following formula
speed (v) = displacement (s) / time (t)
V=S/t
Let's put the dimension of displacement and time
[V] = [S/t]
[V] = L/T
so [V] = LT-¹
NOTE :
Seven base quantities and dimensions .....
Time : T
length : L
mass : M
electric current : I
thermodynamic temperature : θ (theta)
amount of substance : N
luminous intensity : J ( not sure )