2 dimensional lookup

In the spreadsheet attached I have two worksheets A and B . A has the raw data

(a) - Based on the raw data . Values should be in returned in C3 of B worksheet using the lookup formulas . It should look for C2 from Column A of A worksheet & Match it with B3 from Row A of A worksheet .

Incase if there are no values , it should return zeros .

(b) In worksheet B , Cell C2 has the data validation list , each time I update the sheet A I need to manually change the range . Can I get a formula , so that the range is automatically adjusted based on the data in worksheet A .

Thank you