remember
logx+logy=log(xy) so
log2+log(4x-1)=log2(4x-1)=log8x-1
since no base is mentioned, it it base 10
now we have
log 8x-2, base 10=3
means
10 must be raised to the 3rd power to get 8x-2
therfor
10^3=8x-2
1000=8x-2
1002=8x
divide 8 both sides
125.25=x
x=125.25