1)Completed the series of designs that began on July 31 and billed for total design services performed, including the accrued revenues of $800 that had been recognized in an adjusting entry in July $1,400

DR acc.recievable and unearned revenue with 800,600 resp and CR revenue 1,400

2)Paid the amount due for the office equipment purchased last month, $3,000

DR acc.payable 3000 and CR cash 3000

3)Received payment on account for design services performed last month, $2,800.

CR cash 2800 DR acc.receivable 2800

4)Made a partial payment on the utilities bill that was received and recorded at the end of July, $140

DR acc.payable 140 and CR cash 140

I must be doing sth wrong cause I don't get the right figures in the trial balance. There are some other entries as well but I fell comfortable with them so the mistake must be in these...

There's something screwy here. I'm not understanding the transaction to begin with. It doesn't help that I don't know what month you're doing these entries in. (We cannot know how to relate the dates in the transaction to the current date if we don't know what the current date is.)

It sounds like they did $800 of the work on that very first day, July 31. That is the only way anything could have been accrued in a July adjusting entry when the work was started on July 31. That would put the $800 in receivables, not unearned revenue. Unearned revenue is a deferral, not an accrual. (Notice it says "accrued revenues" -- an accrual is when you already did the work but you haven't gotten paid.)

I'm also assuming the $800 is part of the $1400, leaving $600.

In addition to distinguishing between a deferral and an accrual, something else you also have to watch out for is that just because something hasn't been billed doesn't mean it can't be in a receivable account. Receivables represents what is OWED to you. Just because you haven't sent a bill yet doesn't mean it's not owed. It just means you haven't sent the bills yet. So something was earned, and therefore owed to you, as of the end of July, but it hadn't been billed yet. It sounds like they're just now billing the $1400 to the client, but $800 would already be in the accounts. (It would have been better had they done a reversing entry for this.) The revenue of $800 would already have been recorded in July too. In other words, $800 is already recorded in the books, period.

And I don't know what "resp" means.

Thank you vary much for your response!
resp=respectively
These transactions take place in August