一條數學問題(中一程度)

Let x be the age of Mr.chu.
x-3=8(51-x-3)
x-3=408-8x-24
9x =387
　x=43
His son is 51-43=8 years old now.

Set up his son's age is n years old,Mr.Chu is x years old.
n+x=51
8(n-3)=x-3
8n-24+3=x
8n-21=x
n+8n-21=51
9n=51+21
n=72 over 9
n=8
His son is 8 years old now.

x-3=8(51-x-3)
x-3=408-8x-24
9x =387
　x=43
His son is 8 yaears old

中文解釋：
曹先生與他的兒子總歲數是５１歲．３年之後，曹先生比他的兒子大８歲．他的兒子現在多少歲？？？
設他的兒子現在ｐ歲。
３年之後姐係曹生同兒子總歲數是５７　曹生比佢大８歲　姐係曹生３２．５　兒子就２４．５歲　　　
　　　　　　　　

Let X = Mr Chu's age now, and Y = his son's age now.
X + Y = 51
X - 3 = 8 * (Y - 3)
X - 3 = 8Y - 24
X = 8Y -24 + 3
X = 8Y - 21
8Y - 21 + Y = 51
9Y = 72
Y = 8
X = 43

Let the age of Mr. Chu's son is x, the age of Mr. Chu is 51-x
8(x-3)=51-x-3
8x-24=48-x
9x=72
x=8
The age of his son is 8 now