A can make a cupboard in 10 days and B can do it in 50 days. Along with C, they did the job in 6.25 days only. Then in how many days C alone can do the job?
In a certain code language, '+' represents 'x', '-' represents '+', 'x' represents '÷' and '÷' represents '-'. What is the answer to the following question? 642 x 6 ÷ 25 + 4 = ?