If the symbol $$a + b$$ means $$a - b$$, the symbol $$a - b$$ means $$a \times b$$, the symbol $$a \times b$$ means $$a \div b$$, and the symbol $$a \div b$$ means $$a + b$$, then what is the value of the expression: $$10 + 30 - 100 \times 50 \div 25$$? (All operations are to be replaced simultaneously.)

If in a certain code, 'ABCD' is written as 24 and 'EFGH' is written as 1680, then how is 'IJKL' written in that code?

If in a certain code, 'POT' is written as ATOP and 'TRAP' is written as APART, then how is 'ARENA' written in that code?