Use two labeled points to compute the slope $m=\frac{\Delta P}{\Delta t}$.

After you have an equation for $P$ in terms of $t$, substitute $P=60$ and solve for $t$.

In Desmos, enter the points $(1,92)$ and $(5,76)$.

Type y = mx + b and use the two points to determine the line (or use a table with y1 ~ m x1 + b).

Graph the horizontal line $y=60$ and find the $t$-value of the intersection point.

From the graph, the line passes through $(1,92)$ and $(5,76)$.

So the battery level changes by $-4$ percentage points per hour.

Use $P=mt+b$ with $(1,92)$:

So $P=-4t+96$. Set $P=60$ and solve:

Therefore, $t=9$.