[tex]\begin{gathered} \frac{21}{x}=\frac{48}{96} \\ \text{Cross multiplying both sides of the equation,} \\ 21(96)\text{ = 48(x)} \\ x=\frac{21(96)}{48}=21(2)=42 \\ x=42\text{.} \\ \\ \frac{70}{b}=\frac{20}{80} \\ \text{Cross multiplying,} \\ 70(80)=20(b) \\ \text{Dividing both sides by 20.} \\ \frac{70(80)}{20}=\frac{20b}{20} \\ b=70(4)=280 \\ b=280 \\ \\ \frac{50}{20}=\frac{x}{72} \\ \text{Cross multiplying,} \\ 50(72)=x(20) \\ \text{Dividing both sides of the equation by 20,} \\ \frac{50(720}{20}=\frac{x(20)}{20} \\ x=50(36)=1800 \\ x=1800 \end{gathered}[/tex]
In summary, the respective values of the unknown variables in the equations are 42, 280, and 1800.
