I need to use the Immunization Method developed by the British actuary Redington and I also need to do it by hand but I dont know how to do it.

Redignta Im unizoticn mode 2) A npay krows thot thosa firencol debt of 500, ooo thet they must pay in 2umorho / tre voluation interest rate inh",oi. tymmbn.ce ths portfolo with e p ohene of two zcro Covpon ands, with a merturat in tinc of 12 ond 36 months. -Find he mnt cach hand to fully immunizc the oeht and concludk whort yu abaved in that pr troio ycu ob served in that pa tfolic