From $8:30$ to $10:15$ = $1$ hr $45$ min, $1$ hr $45$ min = $105$ min, three $30$-minute parts = $90$ min, $105 - 90$ = $15$ min. 
A certain play has three $30$-minute parts and two intermissions among them. The play started at $8:30$ AM and ended at $10:15$ AM. How many minutes long were the intermissions in total? 
[a] $$10$$ 
[b] $$15$$ 
[c] $$20$$ 
[d] $$25$$ 