What was the "invisible hand" according to adam smith

Definition ; 
the unobservable market force that helps the demand and supply of goods in a free market to reach equilibrium automatically is the invisible hand. 
the phrase "invisible hand" was introduced by adam smith in his book ' the wealth of nations'

12 days because 1/4 is 25% of 100 if 100 is equal to 1 pound then multiply 3 by 4 which equals 12