Question 174466
Let x=sister's present age; x-3 is sister's age three years ago
Then x-3=boy's present; x-6=boy's age three years ago

Now we are told the following
x-6=(2/3)(x-3)  multiply each term by 3
3x-18=2x-6  add 18 to and subtract 2x from each side
3x-2x=12
x=12---------------------sister's present
x-3=12-3=9-----------------boy's present age

CK
9-3=(2/3)(12-3)
6=(2/3)(9)=6
6=6

Does this help???----ptaylor