a) 

$9,7+5,2=14,9$

$10-3,4=6,6$

$5-2,73=2,27$

$2\cdot 8,6=17,2$

$14,8:2=7,4$

b)

$5,25+4,51=9,76$

$100-19,33=80,67$

$20\cdot 3,4$   $=68$

$25,5:5=5,1$

c)

$8,3+4,52=12,82$

$6,38-4,09=2,29$

$100\cdot 5,88=588$

$6,4:0,8=64:8=8$