c: 14,6+1,21+5,4+3,79+14,5
=14,6+5,4+1,21+3,79+14,5
=20+5+14,5
=25+14,5
=39,5
12:
a: \(2\cdot31\cdot12+4\cdot6\cdot41+8\cdot28\cdot3\)
\(=24\cdot31+24\cdot41+24\cdot28\)
\(=24\left(31+41+28\right)=24\cdot100=2400\)
b: \(3,9\cdot\dfrac{13}{10}+\dfrac{0.87}{0.01}\cdot0,39\)
\(=0,39\cdot13+87\cdot0,39\)
\(=0,39\left(13+87\right)=0,39\cdot100=39\)