a) ab+ac=520<=>a(b+c)=520
Dar b+c=52 =>52a=520=>a=520:52=>a=10
b)ab-ac=45<=>a(b-c)=45
Dar b-c=9 =>9a=45=>a=45:9=>a=5
c)ab+ac+70=170<=>ab+ac=170-70<=>ab+ac=100<=>a(b+c)=100
Dar a=25 =>25(b+c)=100=>b+c=100:25=>b+c=4
d)ab-ac-48=2<=>ab-ac=2+48<=>ab-ac=50<=>a(b-c)=50
Dar a=10 =>10(b-c)=50=>b-c=50:10=>b-c=5