4. In a certain code language, '+' represents 'x', '-' represents '+', 'x' represents '÷' and '÷' represents '-'. What is the answer to the following question? 15 - 5 + 25 ÷ 10 = ?
10. In a certain code language, '-' represents 'x', '÷' represents '+', '+' represents '÷' and 'x' represents '-'. Find out the answer to the following question. 7 x 10 ÷ 30 - 2 + 6 = ?