Answer :
We know that we need to bake 6 pound for 138 minutes, then we have the proportion:
[tex]\frac{6}{138}[/tex]Let x be the time we need to bake the 3 pound roast, in this case we have the proportion:
[tex]\frac{3}{x}[/tex]By equating both ratios we have the proportion:
[tex]\frac{3}{x}=\frac{6}{138}[/tex]Now, by simplifying the right side of the proportion we have that:
[tex]\begin{gathered} \frac{3}{x}=\frac{6}{138} \\ \frac{3}{x}=\frac{3}{69} \end{gathered}[/tex]For this proportion to be equal we need that x=69, therefore we need to cook the 3 pound roast for 69 minutes.