#### Answer

$11.30\%$

#### Work Step by Step

First, find the increase in voltage by subtracting the voltage after the surge from the one before it:
$=128 - 115
\\=13$
RECALL:
$\text{percent increase}=\dfrac{\text{increase in value}}{\text{original value}}$
The given problem has:
original value =$115$ volts
increase in value = $13$ volts
Sove for the percent increase using the formula above to obtain:
percent increase
$= \dfrac{13}{115}
\\=0.1130434783
\\=0.1130434783 \times 100\%
\\\approx 11.30\%$
Thus, there was an $11.30\%$ increase in voltage during the surge.