Adult animal weights

Given the following tables, write a SQL query to return the average weight for each adult animal:

table_1

	adult	animal	animal_id	size
0	False	cat	1	M
1	True	dog	2	M
2	False	cat	3	M
3	False	fish	4	S
4	True	dog	5	L
5	True	cat	6	M
6	True	cat	7	M

table_2

	animal_id	weight
0	1	8
1	2	10
2	3	11
3	4	1
4	5	20
5	6	12
6	7	12