Answer :
We have the following ratio scale:
[tex]\frac{\text{REAL}}{\text{DRAWING}}=\frac{10}{3}[/tex]If we move the DRAWING term to the rght hand side, we get
[tex]\text{REAL}=\frac{10}{3}\cdot\text{DRAWING}[/tex]In our case, the line is 15 inches long, then we have
[tex]\text{REAL}=\frac{10}{3}\cdot(15\text{inches)}[/tex]which gives
[tex]\begin{gathered} \text{REAL}=\frac{10\times15}{3}\text{ inches} \\ \text{REAL}=10\times5\text{ inches} \\ \text{REAL}=50\text{ inches} \end{gathered}[/tex]Therefore, the answer is 50 inches.