Answer :
We have the following formula that correlates all those amounts:
[tex]I=\text{PRT}[/tex]Where:
I = Simple Interest
P = Principal
R = Interest Rate
T = Time in Months
We already have 3 of those values. If we just substitute them in the formula, we're going to find the missing one.
Solving for 'P':
[tex]\begin{gathered} 80=P\times0.04\times6 \\ \Rightarrow P=\frac{80}{0.04\times6}=\frac{80}{0.24}=333.33 \end{gathered}[/tex]With this, we have our result. The principal amount is $333.33