Answer:
For l to be parallel to m, angles 87+5x and 10x+17 should be corresponding angles, meaning:
[tex]87^{\circ}+(5x)^{\circ}=(10x+17)^{\circ}.[/tex]Solving the above equation for x, we get:
[tex]\begin{gathered} 87+5x=10x+17, \\ 87-17=10x-5x, \\ 70=5x, \\ \frac{70}{5}=x, \\ 14=x\text{.} \end{gathered}[/tex]x=14.