I'm not a finance guy; heck, I don't even play one on TV (and I didn't stay at a Holiday Inn Express last night either).
However, what you're quoting is an annual return of 10%. The "normal" number I hear for expected return on an endowment is 5%. (In good years, meaning greater than 5% return on the investments, you use the extra to build the lump sum value for future return value.)
If you need $3 MM annually you'd better have a $60 MM endowment would be my non-finance-guy take.