4x/(4x+3y)+3/(1+3y)
=[4x(1+3y)]/[(4x+3y)(1+3y)]+[3(4x+3y)]/[(4x+3y)(1+3y)]
=[4x(1+3y)+3(4x+3y)]/[(4x+3y)(1+3y)]
=(4x+12xy+12x+9y)/(4x+12xy+3y+9y²)
=(16x+12xy+9y)/(4x+12xy+3y+9y²)
4x/(4x+3y)+3/(1+3y)
=[4x(1+3y)]/[(4x+3y)(1+3y)]+[3(4x+3y)]/[(4x+3y)(1+3y)]
=[4x(1+3y)+3(4x+3y)]/[(4x+3y)(1+3y)]
=(4x+12xy+12x+9y)/(4x+12xy+3y+9y²)
=(16x+12xy+9y)/(4x+12xy+3y+9y²)