The default assumption is FIFO - first in, first out. In other words, you sold the oldest shares first. So the 50 shares that you sold were the 20 Day 1 shares and the 30 Day 10 shares.
There is a procedure for designating the specific shares that you are selling. But if the new brokerage does not keep a record of the separate lots, that procedure won't work. Also, to use this procedure you have to tell the broker, at the time of the sale, which lots you are selling.
