Let x be the daughter's age, in years.


Then her brother's age is 2x years.


Then Mrs Thompson age is 4x years.


The condition says that   x + 2x + 4x = 91,   or   7x = 91.


=============> x = 91/7 = 13.


Answer.  Her son is 26 years old.

Let son's age be S

Then mother's is 2S, and daughter's is 

We then get: 

6S + S = 182 ------ Multiplying by LCD, 2  

7S = 182

S, or son is:  

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