5x-20=2(3x-10)=6x-20, eqivalent to 5x-20=6x-20, it s a contradicion; a 2. 4x - 16 - 2x = 2(x - 8), for this 4x - 16 - 2x =4x-2x-16=2x-16, and 2(x-8)=2x-16, so 4x - 16 - 2x = 2(x - 8) is a identity
3. For the case of 6x - 15 = 3(2x - 6)=6x-16, we have 6x - 15 = 6x-16 it is contradiction
4. 5x - 3(x - 4) = 2(x - 6), we know that 5x - 3(x - 4) =5x -3x+12=2x+12, and 2(x-6)=2x-12, so we have 2x+12=2x-12. That is also a cotradiction, finally we have
1.B, 2.A, 3.B, 4.B
