Answer:
new equipment                   50,000 debit
accumulated depreciation  40,000 debit
loss at disposal:                   30,000 debit
                    old equipment               120,000 credit
--to record trade of equipment--
Explanation:
Let's break the transactions into small parts:
We need to remove the old equipment from accounting along with their accumulated depreciation so:
accumulated depreciation 40,000 debit
                    old equipment               120,000 credit
Then, we debit the new equipment at fair value:
new equipment 50,000 debit
Last, assuming the trade has commercial substance: we recognize the gain or loss on sale:
book value of traded equipment: 80,000
fair value of new equipment:         50,000
loss at disposal:                              30,000
<u>Thus, the journal entry will be as follows:</u>
new equipment                   50,000 debit
accumulated depreciation  40,000 debit
loss at disposal:                   30,000 debit
                    old equipment               120,000 credit