Question 1101244
Let 
s = Su-lin's age
m = Mark's age

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We know:
(1)  s = m + 4   (from  "Su-lin is four years older than Mark.")
(2)  2s + 5m = 64   (from "Twice Su-lin's age plus five times Mark's age is equal to 64.")

Thus we have two equations with two unknowns.  Since eq(1) already has s in terms of m, we can substitute "m+4" wherever we see "s" in eq(2).  Re-writing eq(2) with this substitution gives:

2(m+4) + 5m = 64
(2m + 8) + 5m = 64
7m = 56
  m = 8   —> s = m+4 = 8+4 = 12
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Answer:  <b> Su-lin is 12 yrs old, and Mark is 8 yrs old. </b>
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Check:  
(1)  12 = 8+4  (ok)
(2)  2(12)+5(8) = 24 + 40 = 64  (ok)