Database schema:

CREATE TABLE cars (
	id INTEGER NOT NULL -- example: ['2', '1'],
	train_id INTEGER DEFAULT NULL -- example: ['2', '1'],
	position INTEGER DEFAULT NULL -- example: ['2', '1'],
	shape TEXT DEFAULT NULL -- example: ['rectangle', 'bucket'],
	len TEXT DEFAULT NULL -- example: ['long', 'short'],
	sides TEXT DEFAULT NULL -- example: ['not_double', 'double'],
	roof TEXT DEFAULT NULL -- example: ['none', 'peaked'],
	wheels INTEGER DEFAULT NULL -- example: ['2', '3'],
	load_shape TEXT DEFAULT NULL -- example: ['hexagon', 'circle'],
	load_num INTEGER DEFAULT NULL -- example: ['1', '3'],
	PRIMARY KEY (id), 
	CONSTRAINT fk_cars_trains FOREIGN KEY(train_id) REFERENCES trains (id)
)


CREATE TABLE trains (
	id INTEGER NOT NULL -- example: ['2', '1'],
	direction TEXT DEFAULT NULL -- example: ['west', 'east'],
	PRIMARY KEY (id)
)

Question: How many trains with fully loaded head cars are running east?
Evidence: fully loaded refers to load_num = 3; head cars refers to position = 1

SQL:
SELECT COUNT(DISTINCT T1.train_id) FROM cars AS T1 INNER JOIN trains AS T2 ON T1.train_id = T2.id WHERE T1.position = 1 AND T1.load_num = 3