Question 246036
Let x = what the bookseller paid for the book (cost)
Let .25x = profit 

Determine the bookseller's cost:
{{{x + .25x = 180}}} 
{{{1.25x = 180}}}
{{{x = 144}}}
The bookseller paid $144 for the book


Next determine what percentage of profit the bookseller would make at the reduced $171 price.
Let r = the percentage 
Let 144r = the total profit at the reduced price.
(The cost to the bookseller is still $144)


{{{144 + r(144) = 171}}}
{{{144r = 29}}}
{{{r = 29/144}}}
r = .2013 or 20.13%