Given the simple interest formula

From the question, the money deposited is the Principal P=$16,000;
The earned interest I=$4000;
The simple interest rate, r= 6%;
and the time period in years, t= unknown
To find the time unknown time, we substitute for I, P, and r in the formula given. This will give

Since the time given in the options are in months, we will convert time gotten to months

Therefore, the time period in months is 50months