1)(3a-15)/3=3(a-5)/3=a-5
2)(16a-2b)/((8a-b)=2(8a-b)/(8a-b)=2, b≠8a
3)(10-6a)/(3a-5)=2(5-3a)/(3a-5)=-2(3a-5)/(3a-5)=-2, a≠5/3
4)(12a-4)/(1-3a)=4(3a-1)/(1-3a)=-4(1-3a)/(1-3a)=-4, a≠1/3
5)(c-5)/(4c-20)=(c-5)/4(c-5)=1/4=0,25, c≠5
6)(4a-b)/(2b-8a)=(4a-b)/2(b-4a)=-1/2=-0,5, b≠4a