A discrete-time signal $x[n]$ is obtained by sampling an analog signal at $10\;kHz$. The signal $x[n]$ is filtered by a system with impulse response $h[n]=0.5${$ \delta [n]+\delta [n-1]$}. The $3dB$ cutoff frequency of the filter is:
- $1.25\;kHz$
- $2.50\;kHz$
- $4.00\;kHz$
- $5.00\;kHz$