To calculate the magnetic force on a wire, we use the formula:

$ \mathrm{F} = \mathrm{I} \ell \mathrm{B} $

Where:

$ \mathrm{I} $ is the current in the wire (in amperes),

$ \ell $ is the length of the wire (in meters),

$\mathrm{B}$ is the magnetic field strength (in teslas).

Given that:

The current $\mathrm{I}$ is 8 A,

The length of the wire $\ell$ is 4.0 cm, which is 0.04 m (since 1 cm = 0.01 m),

The magnetic field strength $\mathrm{B}$ is 0.15 T,

Substituting these values into the formula gives:

$ \mathrm{F} = 8 \times 0.04 \times 0.15 $

Calculating this:

$ \mathrm{F} = 0.048 \, \mathrm{N} $

To convert this to millinewtons (mN), recall that $1 \, \mathrm{N} = 1000 \, \mathrm{mN}$. Therefore:

$ \mathrm{F} = 48 \, \mathrm{mN} $

Thus, the magnetic force on the wire is 48 mN.