Matthew has a new job as business analyst. He plans

Matthew has a new job as business analyst. He plans to invest 10 percent of his annual salary after the tax into a retirement account at the end of every year for the next 30 years. Suppose that annual return of the investment is 6%, and his current salary before tax is 90k which grow 3% per year. The tax will apply as 15% on the salary up to 50k and it is 20% for the salary interval of 50k and 80k and the tax rate will be 25% for the remaining salary more than 80k (for example if his salary will be 105k, he is paying 15% tax on his first 50k and 20% in the next 30 k and 25% on his next 25k of his salary). then:

a)   Create a spreadsheet which shows Matthew the balance of retirement account for various levels of annual investments and returns.

b)   If Matthew aims to gain $1,000,000 at the end of the 30th year, what percentage of his salary he should put in the investment annually.