Final answer:
The algebraic expression to represent the total salaries for 3 salesmen and y managers is 3x + 3000y.
Step-by-step explanation:
To represent the total salaries for 3 salesmen and y managers, we need to know the salary of a manager. Given that the monthly salary for a salesman is $1000 and the salary of a manager is three times that of a salesman, we can express the salary of a manager as $3000. So, the algebraic expression to represent the total salaries for 3 salesmen and y managers is 3x + 3000y.