How much would it cost Matt to buy 2½ metres? when it is 9.50 per metre

The product of two negative rational numbers is always zero sometimes zero never zero

Adrawer contains 12 identical white socks, 18 identical black socks and 14 identical brown socks. what is the least number of socks you must choose, without looking, to be certain that you have chosen two socks of the same colour?

How to do this , and can some one explain