$a)$  

$9,7+5,2=14,9$  

$10-3,4=6,6$  

$5-2,73=2,27$  

$2\cdot 8,6=17,2$  

$14,8:2=7,4$  

 

$b)$  

$5,25+4,51=9,76$  

$100-19,33=80,67$  

$20\cdot 3,4=68$  

$25,5:5=5,1$  

 

$c)$  

$8,3+4,52=12,82$  

$6,38+4,09=10,47$  

$100\cdot 5,88=588$  

$6,4:0,8=8$