$\text{a)}27+8=35$

$46+9=55$

$38+8=46$

$57+6=63$  

$\text{b)}38-9=29$   

$23-8=15$

$34-6=28$

$21-7=14$  

$\text{c)}57+10=67$

$36+30=66$

$48+40=88$

$69+20=89$  

$\text{d)}68-20=48$

$43-10=33$

$84-40=44$

$51-30=21$  

$\text{e)}40+30=70$

$60+70=130$

$60+60=120$

$90+40=130$  

$\text{f)}100-30=70$

$120-50=70$

$150-70=80$

$140-80=60$