Real easy PEMDAS situation here.
First we handle parentheses and we have a lot of 'em! Starting with the (6 x 5) and (4 + 1):
12 ÷ [(30 ÷ 5 ÷2) + 1]
Now, we handle the division left-to-right inside the parenthesis. 30 ÷ 5 = 6, then 6 ÷ 2 = 3:
12 ÷ (3 + 1)
Last bit of parentheses:
12 ÷ 4
Now divide:
3
EDIT: Changed the word "handled" to "handle." Just a word tense correction.