x5 + 24x4 - 12x3 by 6x
Your equation is wierd. Can you try reformatting it maybe?
Generally the "by" means like a square, such as saying 8 by 8 we assume 8 * 8 (I may be wrong for this guy).
If SOOO:
(x5+24x4−12x3)∗6x=6x6+144x5−72x4