[Background] I am using WPS Spreadsheets to organize September orders. Row 1 is the header, and columns A to E are: Order No., Date, Region, Customer, Amount. The data is in rows 2 to 11 (see below).
[Task] Help me write 3 formulas:
1. Calculate the total amount for the East China region;
2. In column F, calculate how many orders each customer placed in total;
3. In column G, mark orders with an amount of 10000 or more as "Large order", and leave the others blank.
[Requirements]
1. Use formulas that work directly in WPS Spreadsheets; put each formula on its own line so I can copy it;
2. Explain each formula segment by segment;
3. Do not calculate the results for me; only tell me which rows I can manually calculate to verify whether the formulas are correct.

[Spreadsheet]
Order No.,Date,Region,Customer,Amount
A001,2026-09-01,East China,Hengtong Logistics,25600
A002,2026-09-02,South China,Mingde Education,8400
A003,2026-09-03,East China,Yuanjing Design,13800
A004,2026-09-03,North China,Hongyuan Technology,6200
A005,2026-09-04,East China,Hengtong Logistics,4500
A006,2026-09-07,South China,Meijia Decoration,12000
A007,2026-09-08,North China,Qingshi Law Firm,9800
A008,2026-09-09,East China,Mingde Education,3600
A009,2026-09-10,South China,Mingde Education,15200
A010,2026-09-11,East China,Yuanjing Design,7300