For this kind of problem is nneded to replace a letter b by a numerical value. Thne find the missing variable x .
then replace b = 5 in equality
4(5x - 3) = 8 ( x-2)
now eliminate parenthesis, by PEMDAS method
4•5x - 3•4 = 8x - 8•2
20 x - 12 = 8x - 16
now reorganize letters and numerical values
20x - 8x = -16 + 12
12x = -4
then finally x= -4/12 = -1/3