1.
[tex]v = 45\frac{km}{h}\\t = 20 \ min = \frac{20}{60} \ h = \frac{1}{3} \ h\\\\s = v\cdot t\\\\s = 45\frac{km}{h}\cdot\frac{1}{3} \ h\\\\\boxed{s = 15 \ km}[/tex]
2.
[tex]v_{o} = 0\\t =2 \ s\\a = 4\frac{m}{s^{2}}\\\\s = \frac{1}{2}at^{2}\\\\s = \frac{1}{2}\cdot4\frac{m}{s^{2}}\cdot(2 \ s)^{2}\\\\\boxed{s = 8 \ m}[/tex]
3.
[tex]s = 40 \ km\\t = 30 \ min = 0,5 \ h\\\\v = \frac{s}{t}\\\\v = \frac{40 \ km}{0,5 \ h}\\\\\boxed{v = 80\frac{km}{h}}[/tex]
