we have the following:
[tex]\begin{gathered} p=2\cdot w+2\cdot l \\ l=3\cdot w-70 \end{gathered}[/tex]therefore, replacing:
[tex]\begin{gathered} 860=2\cdot w+2\cdot(3\cdot w-70) \\ 860=2w+6w-140 \\ 8w=860+140 \\ w=\frac{1000}{8} \\ w=125 \end{gathered}[/tex]therefore, the answer is:
width is 125 ft and length 305 ft (125*3 -70)
