#### Answer

$53.\overline{3}\%$

#### Work Step by Step

First, find the increase in pressure:
$=115-75
\\=40\text{ lb/in}^2$
RECALL:
$\text{percent increase}=\dfrac{\text{increase in value}}{\text{original value}}$
The given problem has:
original value =$75 \text{ lb/in}^2$
increase in value = $40 \text{ lb/in}^2$
Solve for the percent increase using the formula above to obtain:
percent increase
$= \dfrac{40}{75}
\\=0.5\overline{3}
\\=0.5\overline{3} \times 100\%
\\=43.\overline{3}\%$
Thus, there was an $53.\overline{3}\%$ increase in pressure.