Answer:
The amount they initially invest in 1991 is;

Step-by-step explanation:
Given the expression;

Where;
F= final amount
p=initial investment
r= annual interest rate
t=time in years
Given that;
The amount in the account in 1996 is $4,000, annual interest rate at 3% ;

Making p the subject of formula;

substituting the values;

Therefore, the amount they initially invest in 1991 is;
