I need help with defining this query in MySQL.

I am using a database with attached layout.

For each department, list number of employees born in each decade and their average salaries

salaries emp no INT(11) salary INT(11) from_date DATE | dept, emp ? emp_no INT(11) ? dept no CHAR(4) fromdate DATE to-date DATE Indexes PRIMARY emp no dept no to-date DATE Indexes - PRIMARY emp_no employees emp_no INT(11) birth-date DATE first name VARCHAR(14) last_name VARCHAR(16) gender ENUM(M, F) departments dept_no CHAR(4) dept name VARCHAR(40) hiredate DATE Indexes PRIMARY - Indexes PRIMARY dept name titles emp_no INT(11) title VARCHAR(50) from_date DATE | dept-manager dept_no CHAR(4) emp_no INT(11) from-date DATE to-date DATE Indexes PRIMARY emp no dept no to-date DATE Indexes PRIMARY emp no