19.the difference of four times a number and one is
A.4x-1
B.1-4x
C.4(x-1)
d.4x<1
20.thrice a number a decreased by one is
A.3a-1
B.1-3a
C.3(a-1)
D.3a>1
21. one less than the product of 3 and x is
A.3x<1
B.1<3x
C.1-3x
D.3x-1
pls help​