The formula for calculating the simple interest is given by
[tex]I=Prt[/tex]
Here, P = Principle amount
r = annual interest rate in decimal
t = time in years.
Now, if we invest for months or week then in order to find the simple interest, we must convert the units in years.
Therefore, d is the correct option.
d) Interest rates are annual, so you must convert the units into years.