Rudolph's average balance checking account pays simple interest of 8.4% annually, and he made $6.93 in interest last month. What was Rudolph's average balance last month?

The first thing you should do it to divide the annual interest into 12 months.

8.4% / 12 (Convert the percentage into decimal form)

So, it will be 0.084/12 = 0.007

Then you get the interest last month then divide that amount to the monthly interest.

= 6.93 / 0.007

= $990 is Rudolph's average balance last month.