4 years ago, the respective ratio between $\frac{1}{2}$ of A's age at that time and four times of B's age at that time was 5 : 12. Eight years hence $\frac{1}{2}$ of A's age at the time will be less than B's age at that time by 2 years. Which is B's present age?

In a group of 120 people, one-fifth are men, one-fourth are women and the rest are children The average age of women is five-sixth of the average age of men. If average age of men is 60 years, what is the average age of the group?

A and B started a business by investing Tk. 2,400 and Tk. 3,600 respectively. At the end of 4^th month from the start of the business, C joined with Tk. 'X'. After 8 months from the start of the business, B withdrew Tk. 600. If C's share is Tk. 8,000 in the annual profit of Tk. 22,500, what was the amount the C invested in the business?