(27-2x)(21-2x)=27x21x(1-1/4)解一元二次方程应用题. 要有过程的~~求各位高人快点啊......

(27-2x)(21-2x)=27x21x(1-1/4)
27x21-96x+4x^2=27x21x3/4
4x^2-96x+27x21x1/4=0
x^2-24x+27x21x1/16=0
x^2-24x+144-144+567/16=0
(x-12)^2-1373/16=0
(x-12-√1373/4)(x-12+√1373/4)=0
x=12+√1373/4或x=12-√1373/4