a)

$Ob={\sout{4}}^1\cdot \frac{3}{{\sout{4}}^1}=1\cdot \frac{3}{1}=3m$

$P={\left(\frac{3}{4}\right)}^2=\frac{9}{16}{m}^2$

b)

$Ob=2\cdot 1\frac{3}{5}+2\cdot 3\frac{1}{2}=2\cdot \frac{8}{5}+2\cdot \frac{7}{2}=\frac{16}{5}+\frac{14}{2}=\frac{32}{10}+\frac{70}{10}=\frac{102}{10}=10\frac{2}{10}=10\frac{1}{5}cm$

$P=1\frac{3}{5}\cdot 3\frac{1}{2}=\frac{{\sout{8}}^4}{5}\cdot \frac{7}{{\sout{2}}^1}=\frac{4}{5}\cdot \frac{7}{1}=\frac{28}{5}=5\frac{3}{5}c{m}^2$

c)

$Ob=2\cdot 6\frac{1}{4}+2\cdot 2\frac{2}{5}={\sout{2}}^1\cdot \frac{25}{{\sout{4}}^2}+2\cdot \frac{12}{5}=\frac{25}{2}+\frac{24}{5}=\frac{125}{10}+\frac{48}{10}=\frac{173}{10}=17\frac{3}{10}m$

$P=6\frac{1}{4}\cdot 2\frac{2}{5}=\frac{{\sout{25}}^5}{{\sout{4}}^1}\cdot \frac{{\sout{12}}^3}{{\sout{5}}^1}=\frac{5}{1}\cdot \frac{3}{1}=15m^2$