If a number is divisible by both 2 and 3 then we can say the number is divisible by?

Gthe rational function the quotient of the quantity x minus 4 and the product of the quantity x and 2 times x minus 1 can be expressed as the sum of two partial fractions: the quotient of a and x and the quotient of b and the quantity 2 times x minus 1 . find the value of a - b.