according to figure 3.21, writing in SQL

d. Print the average number of books borrowed per member. Take into account that if an member does not borrow any books, then that member does not appear in the borrowed relation at all. branch(branch name, branch.city, assets) customer (customer_name, customer street, customer_city) loan (loan number, branch name, amount) borrower (customer_name, loan_number) account (account number, branch.name, balance ) depositor (customer_name, account number) Figure 3.19 employee (employee_name, street, city) works (employee_name, company name, salary) company (company.name, city) manages (employee name, manager name) Figure 3.20 member(memb_no, name, age) book(isbn, title, authors, publisher) borrowed(memb.no, isbn, date) Figure 3.21