Extremely nested IF and AND

In my table there are plenty of Data validated cells that are dependent to each other. maybe the below example will help.

cell B2 can only hold these values: {Asia, Africa, America, Europe} if cell B2's value is equal to "Asia" then cell C2 can only contain these values: {China, Japan, India, Iran} if cell B2's value is equal to "America" then cell C2 can only hold {U.S.A, Canada, Brazil, Chile} and so on.

what I want is that IF cell B2 is "Asia" AND cell C2 is "China" THEN cell D2's value should only be "10", AND IF cell B2 is "Asia" and C2 is "Japan", THEN D2 will be 16.

I have plenty of code in the formula bar and apparently I can only nest 20 IF statements inside each other.

If additional information is needed please let me know to provide.