We have been given the formula
[tex]A= P(1+rt)[/tex]
Now, we have been given that
[tex]r=0.03, t=20,A=\$ 8,000[/tex]
On substituting these values in the given formula, we get
[tex]8000=P(1+0.03\cdot 20)\\ \\ 8000=P(1+0.60)\\ \\ 8000= 1.60P\\ \\ P=\frac{8000}{1.60}\\ \\ P=\$5000[/tex]
David will invest a principle amount of $5000