Simple Interest is interest that is computed on the original principal only.
Compound Interest is interest that is computed on the principal and previous interest earned. (You can think of it as "stacking" on top of itself.)
We rounded to four decimal places because it was a percentage. The initial answer is in decimal form and the final answer is in percentage form. In order to have the final answer (in percentage form) rounded to two decimal places, the answer in decimal form must be rounded to four decimal places.
When interest is compounded weekly, m=52 (since there are 52 weeks in a year).
When interest is compounded daily, m=365 (since there are 365 days in a year).