When a retired police officer passes away, he leaves $135,000 to be divided among his two children and five grandchildren. The will specifies that each child is to get twice as much as each grandchild. How much does each get.

from the quetion, we were told that:
The retired police officer has two children and five grand children.
He leaves $135,000
lets divide the $135,000 that he leaves in 7 persons. Recall that each child gets double of what a granchild gets.
Let the amount of child br $x and that of grand children be $y and let us set two equations in x and y and then solve them together for x and y.
A chid amount = 2(grandchild amount).
x = 2y
And sum of 2 children + sum of 5 grandchildren = 135,000
2x + 5y = 135000
2(2y) + 5y = 135000
4y + 5y = 13500
9y = 135000
divivide both sides by 9
9y /9 = 135000/9
y = 135000/9
y = 15000
So, each grandchild gets $15000.
And accordingly child gets 2(15000) = $30000
That is, each grandchild gets $15000 and child gets $30000