设每件衬衫应降价x元
(45-x)(20+4x)=2100
900+180x-20x-4x^2=2100
225+45x-5x-x^2=525
x^2-40x+300=0
(x-10)(x-30)=0
x1=10 x2=30
答:每件衬衫应降价10或30元
设每件衬衫应降价x元
(45-x)(20+4x)=2100
900+180x-20x-4x^2=2100
225+45x-5x-x^2=525
x^2-40x+300=0
(x-10)(x-30)=0
x1=10 x2=30
答:每件衬衫应降价10或30元