Question 1110899
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L = 9 + 3*S,             (1)

L + 5 = 6 + 2*(S+5).     (2)



Substitute (1) into (2).  You will get

9 + 3*S + 5 = 6 + 2S + 10,

S = 6 + 10 - 9 - 5 = 2.


Thus we found that the son is 2 years old.

Then Lucas (= the father of his son) is 9 + 3*2 = 9 + 6 = 15 years old.
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