Series: 0..10...24...56...112...190....280 (missing number and working out shown in bold print)
1st dif:...10..14...32...56.....78.....90
2nd dif:......4....18...24....22.....12
3rd dif:..........14....6....-2.....-10
4th dif:...............-8...-8....-8 (constant difference)