Nilai a + 10 = …a.25b.35c.45d.75

280 = (180 – (a + 13)) + (180 – (2a – 8))
180 – a – 13 + 180 – 2a + 8 = 280
355 – 3a = 280
3a = 355 – 280 = 75
a = 25

a+10 = 25+10 = 35 (B)