Can someone please help me with the following problem?

5 years ago, mother was seven times as old as her son & 5 years hence, she will be three times as old as her son. Find their present ages.

This is what I tried:

Let present age of son be x.

Five years ago:

Son's age = x-5

Mother's age = 7(x-5)

Five years hence (means 5+5=10 years hence):

Son's age = x-5+10 = x+5

Mother's age = 7(x-5)+10 = 7x-35+10=7x-25

Five years hence, mother will be three times as old as her son. So

x+5 = 3(7x-25)

x+5 = 21x-75

20x = 80

x = 4

But the answer is wrong! What am I doing wrong?

Thanks,

Ron