通分
公分母是(4x+3y)(1+3y)
所以原式=[4x(1+3y)+3(4x+3y)]/(4x+3y)(1+3y)
=(4x+12xy+12x+9y)/(4x+3y)(1+3y)
=(12xy+16x+9y)/(4x+12xy+3y+9y^2)