a)
[tex]90\frac{m}{s} = 90\cdot\frac{\frac{1}{1000}km}{\frac{1}{3600}h}}=90\cdot3,6 \ \frac{km}{h} = 324\frac{km}{h}\\\\20\frac{m}{s} = 20\cdot\frac{\frac{1}{1000}km}{\frac{1}{3600}h} = 20\cdot3,6 \ \frac{km}{h} = 72\frac{km}{h}\\\\40\frac{m}{s} = 40\cdot\frac{\frac{1}{1000}km}{\frac{1}{3600}h} = 40\cdot3,6 \ \frac{km}{h} = 144\frac{km}{h}[/tex]
b)
[tex]108\frac{km}{h} = 108\cdot\frac{1000 \ m}{3600 \ s} = 30\frac{m}{s}\\\\180\frac{km}{h} = 180\cdot\frac{1000 \ m}{3600 \ s} = 50\frac{m}{s}\\\\144\frac{km}{h} = 144\cdot\frac{1000 \ m}{3600 \ s} = 40\frac{m}{s}[/tex]
