Doing two counts on a single table in a single query
You can use CASE statement for this scenario:

SELECT count(*) AS total_agents, 
       SUM(CASE WHEN active = 't' THEN 1 ELSE 0 END) AS active_agents
FROM Agent;


Sample execution with sample data:

CREATE TABLE Agent (Id INT, Active CHAR(10));

INSERT INTO Agent (Active)
VALUES ('a'), ('b'), ('t'), ('c'), ('t'), ('d');

SELECT count(*) AS total_agents, 
       SUM(CASE WHEN active = 't' THEN 1 ELSE 0 END) AS active_agents
FROM Agent;