Question 1202759
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Apple, Lea and Sarah are siblings. Apple is turning 12 next year. 
Lea's age in 8 year plus Sarah's age in 3 years is equal to four times Apple's age next year. 
What is the {{{highlight(cross(some))}}} <U>SUM</U> of their ages in six years.
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Since "Apple is turning 12 next year" (given), Apple's age is 11 years now.
So, we write  A = 11.


Lea's   age in 8 years will be  (L+8) years.

Sarah's age in 3 years will be  (S+3) years.


Since "Lea's age in 8 year plus Sarah's age in 3 years is equal to four times 
Apple's age next year", we can write this equation

    (L+8) + (S+3) = 4*12,

which implies

    L + S = 48 - 8 - 3 = 37 years.


Then the sum of the ages of the three siblings this year is 

    A + L + S = = A + (L + S) = 11 + 37 = 48 years.


In 6 years later, the sum of their ages will be

    48 + 3*6 = 48 + 18 = 66 years.    


<U>ANSWER</U>.  The sum of their ages in six years will be 66 years.
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Solved.