Step-by-step explanation:
[tex]1.\ \dfrac{x}{16}=\dfrac{45}{40}\qquad\text{cross multiply}\\\\40x=(16)(45)\\\\40x=720\qquad\text{divide both sides by 40}\\\\\boxed{x=18}\\\\======================[/tex]
[tex]2.\ \dfrac{x}{5}=\dfrac{1}{4}\qquad\text{cross multiply}\\\\4x=(1)(5)\\\\4x=5\qquad\text{divide both sides by 5}\\\\\boxed{x=\dfrac{4}{5}}\\\\======================[/tex]
[tex]3.\ \dfrac{2.5}{10}=\dfrac{x}{50}\qquad\text{cross multiply}\\\\10x=(2.5)(50)\\\\10x=75\qquad\text{divide both sides by 10}\\\\\boxed{x=7.5}\\\\======================[/tex]
[tex]4.\ \dfrac{x}{6}=\dfrac{2}{9}\qquad\text{cross multiply}\\\\9x=(6)(2)\\\\9x=12\qquad\text{divide both sides by 9}\\\\x=\dfrac{12}{9}\\\\x=\dfrac{12:3}{9:3}\\\\\boxed{x=\dfrac{4}{3}}[/tex]
