设u=(3x-y)/4
则u'=3/4-y'/4
代入原方程得：3-4u'=u
即u'=(3-u)/4
du/(u-3)=-dx/4
积分：ln|u-3|=-x/4+c1
即u-3=ce^(-x/4)
(3x-y)/4-3=ce^(-x/4)
得：y=3x-12-4ce^(-x/4)