[tex]Dane:\\s = 30 \ km\\t = 45 \ min = \frac{45}{60} \ h = \frac{3}{4} \ h\\Szukane:\\v_{sr} = ?\\\\Rozwiazanie\\\\v_{sr} = \frac{s}{t}\\\\v_{sr} = \frac{30 \ km}{\frac{3}{4} \ h}=30\cdot\frac{4}{3} \ \frac{km}{h}\\\\\boxed{v_{sr} = 40\frac{km}{h}}[/tex]
