#### Answer

3000 dollars are needed as principal.

#### Work Step by Step

The interest formula is: I = P $\times$ r $\times$ t.
To find the principal, or P, we divide I by r $\times$ t.
So, P = $\frac{I}{r\ \times\ t}$
r = 5% = 0.05
t = 4
I = 600
Substitute these values in the formula to obtain:
P = $\frac{600}{0.05\ \times\ 4}$
P = $\frac{600}{0.20}$
P = 3000 dollars.