Let H be Huang's age. Translating the sentence to an equation gives
H+7=2(H-1)
That is: in 7 years, when Huang's age is 7 more than it is now, his age will be 2 times what it was last year (when it was one less than it is now, or H-1)
Solving for H:
H+7=2H-2
H+7-2H+2=0
-H+-7-2=0
-H=-9
H=9
Now let's check: In 7 years he will be 9+7=16
Last year he was 8 and 16 is indeed twice this age
