How Does it Work?
Multiplying the top and bottom of a fraction by the same amount doesn't change its value.
Step 1: Multiply the top and bottom of the first fraction by the bottom number of the second fraction.
8 × 3 = 2
12 × 3 3
Step 2: Multiply the top and bottom of the second fraction by the bottom number the first fraction had.
8 × 3 = 2 × 12
12 × 3 3 × 12
And Magic! The bottom of both fractions is now 12 × 3
Step 3: We can get rid of the 12 × 3 (as we are dividing both sides by the same amount) and the equation is still true:
8 × 3 = 12 × 2
Job Done!
In practice, though, it is easier to skip the steps and go straight to the "cross-multiplied" form.