Answer
$90s$
Work Step by Step
First of all, determine your velocity relative to the walkway:
$\vec{v_{yw}}=\frac{\Delta x}{\Delta t}\hat x=(\frac{-85m}{68s})\hat x=(-1.3\frac{m}{s})\hat x$
Now find your velocity relative to the ground:
$\vec{v_{yg}}=\vec{v_{yw}}+\vec{v_{wg}}$
Where $\vec{v_{yg}},\vec{v_{yw}},\vec{v_{wg}}$ represent your velocity relative to ground, relative to walkway, and walkway relative to ground, respectively.
We plug in the known values to obtain:
$\vec{yg}=(-1.3\frac{m}{s})\hat x+(2.2\frac{m}{s})\hat x=(0.9\frac{m}{s})\hat x$
Now we can find the required time
$t=\frac{\Delta x}{v_{yg}}$
$\implies t=\frac{85}{0.9}$
$t=90s$
