Accounting question

Sky Probe sells state- of- the- art telescopes to individuals and organizations interested in studying the solar system. At December 31 last year, the companys inventory amounted to $ 250,000. Dur-ing the first week of January this year, the company made only one purchase and one sale. These transactions were as follows:

Jan. 2 Sold one telescope costing $ 90,000 to Central State University for cash, $ 117,000.

Jan. 5 Purchased merchandise on account from Lunar Optics, $ 50,000. Terms, net 30 days.

A. Prepare journal entries to record these transactions assuming that Sky Probe uses the perpetual inventory system. Use separate entries to record the sales revenue and the cost of goods sold for the sale on January 2.

B. Compute the balance of the Inventory account on January 7.

C. Prepare journal entries to record the two transactions, assuming that Sky Probe uses the peri-odic inventory system.

D. Compute the cost of goods sold for the first week of January assuming use of a periodic inven-tory system. Use your answer to part b as the ending inventory.

E. Which inventory system do you believe that a company such as Sky Probe would probably use? Explain your reasoning.

Here is what I got.
A) Perpetual Inventory System
Jan 2. Cash (not sure if this is what I should title the account) Debit 117,000
Sales (credit) 117,000
Jan. 5 inventory -debit 50,000
Account payable (Lunar Optics) credit 50,000
Jan. 2 cost of goods Sold - debit 90000
Inventory - Credit 90000
SHOULD I BE MAKING AN ADDITION ENTRY FOR SALES REVENUE FOR JAN 2?

For B I am confused as to how I should compute the balance of Inventory?

C) Periodic Inventory System
CASH (Again not sure if this should be the title) debit 117,000
Sales Credit 117,000
Jan. 5 Purchases Debit 50000
Accounts Payable (Lunar Optics) Credit 50000
Am I missing anything else?

Part D
Inventory end of dec. 250000
Add: Purchases 50000
Cost of Goods Available for sale 300,000
Les Inventory 90000
Cost of Goods Sold 210,000
Is this how I compute the cost of goods for the first week of jan.?

D) Because Sky Probe sells telescopes for a high cost and has only made one sale transaction so far this year, I would say it is possbile they use a perpetual inventory system.

Any help would be appreciated. THanks so much.