Question 936560
Robert is 15 years older than his sister Stan. (imagine someone naming a girl "Stan")
r = s + 15
:
 However "y" years old ago, Robert was twice as old as Stan.
r - y = 2(s - y)
 If Stan is now "b" years old and b > y, 
s = b, then r = (b+15)
In the 2nd equation, replace r with (b+15) and s with b
(b+15) - y = 2(b - y)
b + 15 - y = 2b - 2y
15 = 2b - b - 2y + y
15 = b - y
Find the value of (b - y) = 15
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