Extract the folder "texture.N172RK" into your [FSX]\SimObjects\Airplanes\A2A_C172 folder.

Add the following to the aircraft.cfg file, changing "XX" to the next number in sequence. 

--

[fltsim.XX]
title=C172R N172RK
sim=C172
model=
panel=
sound=
texture=N172RK
kb_checklists=C172_check
kb_reference=C172_ref
atc_id=N172RK
ui_manufacturer=A2A Cessna
ui_type="C172R Skyhawk"
ui_variation="N172RK"
ui_typerole="Single Engine Prop"
ui_createdby="A2A Simulations Inc."
description="Repaint by Calvin Diogo/CharlieDelta Textures."

--