So make sure that two building blocks are built at the same time.
Sticking to pies is the same principle.
Need classmate 1 classmate 2 classmate 3.
Same as 65438 +0 column+same as 2 column 4.
Then use 1 castle +3 train 4.
Then there is Tang 2 Castle+Tang 3 Castle 4.
So it is 4*3= 12 (minutes)
The rule is that you put a pie on your math book.
I forgot the formula. Sorry, give it to me personally ~ ~ ~
If you don't understand, you can ask.