a)

$3,2\cdot \left(1\frac{1}{2}+7,6\right)=3,2\cdot \left(1,5+7,6\right)=3,2\cdot 9,1=29,12$

b)

$\left(3,18-2\frac{3}{4}\right)\cdot 0,7=\left(3,18-2,75\right)\cdot 0,7=0,43\cdot 0,7=0,301$