X Co Books

No. 1 & 3 - As "saver" mentioned memo only.

2) As "westlife" mentioned
Dr. Cash/Cash in Bank - 20,000
Cr. Unearned income --- 20,000

4) Dr. Receivable (Y Co) - 10,000
Cr. Cash/Cash in Bank - 10,000

5) Dr. Cost/Exps A/C ----- 25,000
Cr. Receivable (Y Co) - 10,000
Cr. Payable (Y co) ---- 15,000

6) Dr. Receivable -------- 30,000
Dr. Unearned Income --- 20,000
Cr. Income/Revenue ---- 50,000