SOLUTION: Christian deposits P 300 at the end of each quarter in his savings account. If the account earns 5.75% yearly, how much money will he has in 4 years?

It is a classic Ordinary Annuity saving plan. The general formula is 


    FV = ,    (1)


where  FV is the future value of the account;  P is your quarterly payment (deposit); 
r is the quarterly percentage yield presented as a decimal; 
n is the number of deposits (= the number of years multiplied by 4, in this case).


Under the given conditions, P = 300;  r = 0.0575/4;  n = 4*4 = 16.  
So, according to the formula (1), Christian will get at the end of the 4-th year


    FV =  =  P5353.89.


Note that Christian will deposit only  4*4*P300 = P4800 in 4 years.  
The rest is what the account earns/accumulates in 4 years.