How much interest is earned on a principal amount of $400 invested at an interest rate of 5% for 3 years

With alll of except for the 2 that i did already

Determine domain and range, largest open interval, and intervals which function is continuous.

How many quarts of a 50% solution of acid must be added to 20 quarts of a 20% solution of acid in order to get a 40% solution of acid?