Question 329852
Let D=David's age now and d=daughters age now.

David is twice her age: D=2d

4 years from now, David's age: D+4

is 3 times his daughters age 6 years ago: 3(d-6)

So, put it together and we have D+4=3(d-6)

Make the sub D=2d and we have 2d+4=3(d-6)

d=22 and D=44