Answer
$t = 113~min$
Work Step by Step
We can write an expression for the original power:
$P_0 = \frac{V^2}{R}$
We can write an expression for the new value of the power:
$P = \frac{(0.940~V)^2}{R} = 0.8836~P_0$
We can find the new time to provide the required energy $E$:
$t = \frac{E}{P}$
$t = \frac{E}{0.8836~P_0}$
$t = 1.1317~\frac{E}{P_0}$
$t = (1.13)~(100~min)$
$t = 113~min$
