The simple interest can be calculated as:
I = Prt
where,
I = Interest due
P = Principal Amount = $950
r = Interest rate = 13% = 0.13
t = time in years = 120/360 year = 1/3 (If not stated, a year is considered equal to 360 days in such cases)
Using the values, we get:
I = 950 x 0.13 x 1/3 = $ 41.17
Thus, $41.17 interest will be due for 120 days