The formula for determining simpe interest is expressed as
I = PRT/100
where
I = interest
P = principal or initial amount deposited
R = interest rate
T = number of years
From the information given,
T = 4
R = 5
Recall,
Total amount = principal + interest
This means that
Interest = Total amount - principal
I = 20000 - P
Thus, we have
20000 - P = P * 5 * 4/100
20000 - P = 0.2P
0.2P + P = 20000
1.2P = 20000
P = 20000/1.2
P = 16666.67
The amount needed to be deposited is $16666.67