How to make HBF-based Narrow-band LPF ?

Based on the FIR (Finite Impulse Response) filter structure; use the designed Half-Band Filter (HBF) in section 4 (HBF-based LPF) as one stage in a multi-stage LPF with decimation-by-2 after each stage. This multi-stage LPF provides . Show how many stages of HBF will be used and plot the magnitude response and phase response for each stage and the whole LPF magnitude response