A+b = 510 (i)
a/8 = b/9 (ii)

(i) b = 510-a
(i) em (ii) a/8 = (510-a)/9
9a = 8.(510-a)
9a = 8.510 - 8a
9a+8a = 8.510
17a = 8.510
a = (8.510)/17
a = 8.(510): 17
a = 8.30
a = 240
(i) b = 510-a
b = 510-240
b = 270