Of 1,000 customers, 200 had payments greater than 30 days last month. This month, there are 1,100

Question:

Of 1,000 customers, 200 had payments greater than 30 days last month. This month, there are 1,100 customers, of which 230 had payments greater than 30 days.
a. Estimate the fraction late for last month and this month.
b. Construct a 90% confidence interval on the difference in the percentage of late payments.
c. What can you conclude?