I would not buy the Iphone 7 because they did not take out the correct percent off. 25% would be .25, so .25 x 675=168.75 should be taken off the price to make it sale price $506.25.
The store had the computer take only 20% off of the price because:
675-540=135 for the amount they took off.
% x 675=135
%=135/675
%=.2 or 20%