F is proportional to 1/x^2
distance = x
A reduction of 25 percent = 0.75x
Let’s put this in place of x
F = 1/(0.75x)^2
And simplify
F = 1/0.5625x^2
So you need to find the percentage increase from 1/x^2 to 1/0.5625x^2
So what does 1/x^2 multiply by to give 1/0.5625x^2
Written as an equation it is y/x^2 = 1/0.5625x^2
Multiply both sides by x^2
y = 1/0.5625
y = 1.778 (rounded to 3 decimal points)
So the decimal multiplier is 1.778 and so the percent increase is approximately 77.8%