Answer:
Ron's principal balance at the start of June was $22,909.09
Explanation:
The simple interest formula is given by:

In which E are the earnings(interest), P is the principal(the initial amount of money), I is the interest rate(yearly, as a decimal) and t is the time, in years.
In this problem, we have that:
His June interest is $210, so
.
The current rate of interest is 11%, so

June has 30 days, and we are assuming 360 days an year. So

We want to find P




Ron's principal balance at the start of June was $22,909.09