Question 1184480
Dim the first stamps of A, B, C
with a,b,c.
Step 1: A: a
B: {{{7/9}}}b
C: {{{2/9}}}b + c
Step 2: A 3/5 * 7/9 b + a = 21/45 b + a
B : 2/5 * 7/9b = 14/45 b [1]
Step 3: A : {{{2/3}}} ({{{21/45}}}b + a)
= {{{2/3}}}a + {{{14/45}}}b [2]
end: C : 600
B : 600 - 460 = 140 [1]
A: 140 + 240 = 380 [2]

=>    [1] = [1]   => a = 360
        [2] = [2]   => b = 450

{{{highlight_green(matrix(1,4, b - a, "=", 90, stamps))}}}</pre>