Question

Q. # 15 please help to solve

Answer 1

Since
 $18x^3=2\cdot 3\cdot 3\cdot x\cdot x\cdot x \\ \\ 30x^5=2\cdot 3\cdot 5\cdot x\cdot x\cdot x\cdot x\cdot x$
you can see that common expression is 
$2\cdot 3\cdot x\cdot x\cdot x=6x^3$.
Answer: Correct choice is A.