associative property is dealing with parentahsees and orders
it is
a(bc)=(ab)c and
a+(b+c)=(a+b)+c
so we want the multiplication one
given
(10)(5x)(7)
we can arragnge these a number of ways (we should use commutative property, but whatever)
first one works, the 7 was moved to front
2nd is wrong, that is a wierd version of the distributive
3rd is right, 5x was moved to the front
4th is wack, no bueno
answer is 1st and 3rd options