Answer: 0.071%
Explanation:
To get from $3.50 - $3.75, there was an increase of $0.25.
(Sorry if I'm getting the currency bit wrong, I'm British.)
Divide 0.25 by the original cost of 3.50, and you get:
0.07142857142857142857142857142857
Round this and you get a 0.071% increase