If force ( F ) , velocity ( V ) and time ( T ) are considered as...

The dimensional formula of force is

$F = ML{T}^{- 2}$

The dimensional formula of velocity is

$V = L{T}^{- 1}$

The formula for density is

Density $= \dfrac{M}{{L}^{3}} = M{L}^{- 3}$

Comparing the density dimensions with the assumed fundamental quantities in the question,
$M{L}^{- 3} = {\left[F\right]}^{x}{\left[V\right]}^{y}{\left[T\right]}^{z} ⇒ M{L}^{- 3} = {\left[ML{T}^{- 2}\right]}^{x}{\left[L{T}^{- 1}\right]}^{y} [ T{]}^{z} ⇒ M{L}^{- 3} = {M}^{x}{L}^{( x + y )}{T}^{- 2x - y + z}$

Comparing the exponents,
$x = 1 . . . ( i ) x + y = - 3 . . . ( ii ) - 2x - y + z = 0 . . . ( iii )$

Solving equations (i), (ii) & (iii), we get

$y = - 4, z = - 2$.

The dimensions of density $= F{V}^{- 4}{T}^{- 2}$.