If I Is the Interest Rate and X Is the Number

If i is the interest rate and X is the number of dollars to be received after t years, the formula to calculate the present value of a future payment is

A) $( 1 + i ) ^ { t } X$
B) $X / ( 1 + i ) ^ { t }$
C) $i ^ { t } / ( 1 + X )$
D) $( X /i ) t$