Alan: a
Bob: b
Charlie: c
"Alan is twice the height of Bob" a = 2*b
"Charlie is 40cm taller than Bob" c = b+40cm
Total height: a+b+c = 410cm
2*b + b + b+40cm = 410cm = 4b + 40cm [-40cm]
4b = 410cm - 40cm = 370cm [/4]
b = 370cm/4 = 92.5cm
Insert b = 92.5cm into a = 2*b:
a = 2*92.5cm = 185cm
Insert b = 92.5cm into c = b+40cm:
c = 92.5cm + 40cm = 132.5cm
[input]solve(a+b+c=410[cm], a=2*b, c=b+40cm,a,b,c)[/input]
+6 
+104 
