計數勁in!!!

3x articles cost (7x+2) dollars, (4x+1) similar articles cost (12x+2) dollars. Find x
assume each artivle have the samme cost
(7x+2)/(3x)=(12x+2)/(4x+1)
(7x+2)(4x+1)=3x(12x+2)
28x^2+15x+2=36x^2+6x
8x^2-9x-2=0
x=1.3151 or x=-0.1901 (reject)