Question 1030858
Call their ages NOW, m and f.  Then we write
m = f + 21
Nine years from now,
m + 9 = 2(f + 9)
Substitute the first one into the second and get
f+21 + 9 = 2(f + 9)
f + 30 = 2f + 18
Now subtract 18 and subtract f and get
f + 12 = 2f
f = 12
Thus Michelle is 33.