in plain and short, we'll simply divide 180 by (4+5+9), and give 4 pieces of those to the ratio of 4, 5 to the ratio of 5 and 9 to the ratio of 9, thus
[tex]\bf \cfrac{180}{4+5+9}\implies 10\qquad \qquad \qquad \qquad \qquad \stackrel{4\cdot 10}{40}~:~\stackrel{5\cdot 10}{50}~:~\stackrel{9\cdot 10}{90}[/tex]
