compare the 3 average productivity indices for the whole of 2022 (12 months) with the 3 average indices of July-September (only 3 months) of 2023. a) What is the percentage change for each index? (12 marks) b)Why do we use only 3 late months in 2023? *USE EXCEL and Provide formulas Please

Period	Sales ($'000's)	Labour ($'000's)	Material ($'000's)	Other Costs ($'000's)
Jan-22	250	63	104	65
Feb-22	252	62	102	66
Mar-22	282	65	103	64
Apr-22	255	64	106	66
May-22	263	66	103	63
Jun-22	270	69	104	65
Jul-22	265	68	102	64
Aug-22	262	66	108	67
Sep-22	254	69	107	66
Oct-22	259	75	109	65
Nov-22	265	76	115	69
Dec-22	268	77	120	70
Jan-23	255	51	156	64
Feb-23	265	47	150	63
Mar-23	275	35	149	64
Apr-23	290	31	144	65
May-23	284	30	146	63
Jun-23	286	31	147	65
Jul-23	295	29	148	64
Aug-23	292	29	148	63
Sep-23	301	31	150	65