a: \(\left(5,12+7,28\right)\cdot4,15+\left(7,85-6,4\right)\cdot12,4\)
\(=12,4\cdot4,15+1,45\cdot12,4\)
\(=12,4\cdot\left(4,15+1,45\right)=12,4\cdot5,6=69,44\)
b: \(2,86\cdot4+3,14\cdot4-6,01\cdot5+3^2\)
\(=4\cdot\left(2,86+3,14\right)-30,05+9\)
\(=4\cdot6+9-30,05=33-30,05=2,95\)
