How would I use Excel to solve this problem? "Given the following data and seasonal index:

MONTH SALES YEAR $1$ YEAR $2$ Jan $88$ Feb $79$ Mar $56$ Apr $1011$ May $912$ June $1216$ July $1520$ Aug $2025$ Sept $44$ Oct $32$ Nov $87$ Dec $99$

a$)$compute the seasonal index using only year $1$ data and b$)$determine the deseasonalized demand values using year $2$ data and year $1\text{'}$s seasonal indices.

I would like more emphasis on the instruction of solving in Excel so that I understand, not just a cut and paste answer. Thank you.