$\text{a)}$

$45\text{min}=\frac{45}{60}\text{godz}=\frac{3}{4}\text{godz}$

$25\text{min}=\frac{25}{60}\text{godz}=\frac{5}{12}\text{godz}$

$1\text{s}=\frac{1}{60}\text{min}=\frac{1}{60}\cdot \frac{1}{60}\text{godz}=\frac{1}{3600}\text{godz}$

$15\text{s}=15\cdot \frac{1}{3600}\text{godz}=\frac{1}{240}\text{godz}$

 

$\text{b)}$

$200\text{m}=\frac{200}{1000}\text{km}=\frac{1}{5}\text{km}$

$8\text{m}=\frac{8}{1000}\text{km}=\frac{4}{500}\text{km}=\frac{2}{250}\text{km}=\frac{1}{125}\text{km}$

$125\text{cm}=\frac{125}{100}\text{m}=1,25\text{m}=\frac{1,25}{1000}\text{km}=\frac{125}{100000}\text{km}=\frac{5}{4000}\text{km}=\frac{1}{800}\text{km}$

$1500\text{cm}=\frac{1500}{100}\text{m}=15m=\frac{15}{1000}\text{km}=\frac{3}{200}\text{km}$