$\text{a)}$

$8-0,7=7,3$

$5-3,2=1,8$

$6-0,42=5,58$

$7-0,53=6,47$

 

$\text{b)}$

$4,7-0,8=3,9$

$2,5-1,7=0,8$

$8,2-4,5=3,7$

$7,6-2,9=4,7$

 

$\text{c)}$

$2,83-0,3=2,53$

$6,58-3,5=3,08$

$9,41-2,1=7,31$

$7,39-5,2=2,19$

 

$\text{d)}$

$3,5-0,42=3,08$

$5,4-1,03=4,37$

$9-2,25=6,75$

$7-3,45=3,55$