A+B+C=1260
A/B = 2/3 cross multiply 3A = 2B and B = 3/2 * A
B/C = 4/5 cross multiply 5B = 4C and C = 5/4 * B
Solve the first equation for A by substituting in B and C in terms of A.
B = 3/2 * A and C = 5/4 * B = 5/4 * 3/2 * A = 15/8 * A
A + (3/2)A + (15/8)A = 1260
(8A + 12A + 15A)/8 = 1260
35A = 10080
A=288
B = 3/2 * A = 3/2 * 288 = 432
C = 5/4 * B = 5/4 * 432 = 540
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