a)

$34,6+23,4=58$

$16,7-18,4=-\left(18,4-16,7\right)=-1,7$

$10\cdot 43,08=430,8$

$5\cdot 12,1=60,5$

$678,33:100=6,7833$

$10:2,5=100:25=4$

b)

${0,5}^2=0,25$

${0,1}^2=0,01$

${0,1}^3=0,001$

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

${\left(1\frac{1}{2}\right)}^2={\left(\frac{3}{2}\right)}^2-\frac{9}{4}$

${\left(1\frac{1}{3}\right)}^2={\left(\frac{4}{3}\right)}^2=\frac{16}{9}$

${\left(-0,3\right)}^2=0,09$

${\left(-0,2\right)}^3=-0,008$

${10}^2\cdot 0,07=100\cdot 0,07=7$