To arrive into the final equation 8j-3k, we must multiply both sides of the original equation with the least common denominator (lcd) of the two fractions.
In this case, the lcd is 12. Multiplying that to both sides will result in:
(2/3j - 1/4k = 5/2) *12
(2/3j)*12 – (1/4k)*12 = (5/2)*12
8j – 3k = 30
