Rewrite y6 as (y3)2.
Let u=y3. Substitute u for all occurrences of y3.
Factor u2-4u-12 using the AC method.
Consider the form x2+bx+c. Find a pair of integers whose product is c and whose sum is b. In this case, whose product is -12 and whose sum is -4.
Write the factored form using these integers.
Replace all occurrences of u with y3.