[tex]\it a)\ \dfrac{x}{20} = \dfrac{^{4)}4}{\ 5} \Rightarrow \dfrac{x}{20}=\dfrac{16}{20} \Rightarrow x=16\\ \\ \\ b)\ \dfrac{45}{y}=\dfrac{^{5)}9}{\ 5}\Rightarrow \dfrac{45}{y}=\dfrac{45}{25} \Rightarrow y=25\\ \\ \\ c)\ \dfrac{a}{6}=13 \Rightarrow a=6\cdot13 \Rightarrow a= 78\\ \\ \\ c)\ \dfrac{a}{6}=13 \Rightarrow \dfrac{a}{6}=\dfrac{^{6)}13}{1} \Rightarrow \dfrac{a}{6}=\dfrac{78}{6} \Rightarrow a=78\\ \\ \\ d)\ \dfrac{2}{3b}=\dfrac{\ 10^{(5}}{15} \Rightarrow \dfrac{2}{3b}=\dfrac{2}{3} \Rightarrow 3b=3[/tex]
⇒ b=1
