If <em>d</em> is being multiplied by a fraction, simply multiply both sides of the equation by the reciprocal of that fraction to get <em>d</em> by itself.
So in this problem, since <em>d</em> is being multiplied by 3/2,
we multiply both sides of the equation by 2/3.
On the left, (2/3)(3/2) cancels out and on the right, if you multiply 12 by 2/3, the 12 and 3 reduce to 4 and 1 so we have (4)(2) which is 8.