（17.5-1.5×5）/x+5= 2/3*[(27.5-1.5×5)/x+5]
10/x +5 = 2/3*[20/x +5]
(10- 2/3*20)/x = (2/3-1)*5
-10*1/3x = -1/3 *5
x=1/2