Question 1839
Definitions:

Let m = mothers age today
Let d = daughters age today

So, we know m = 6d  --1
and  (m+20) = 2(d+20)  --2

sub 1 into 2, giving (6d+20) = (2d+40)
then re-arragne to give 4d = 20. therefore d=5 and hence m=30

cheers
Jon