35500

For levels 1-2 its a lot easier as its the nth term. whatever the difference is between the linear sequence is what you have to multiply n with. Then see how much you have to shift up/down to get to the sequence.
e.g 7, 12, 17, 22, 27
The difference is 5 then you have to shift down 2 so... 5n-2
e.g.2 28, 43, 58, 73, 88
The difference is 15 and you have to shift up 13 so... 15n+13

Levels 3-4 is a lot harder as the sequences aren't the first five. The rules are more or less trial and error, see what the numbers roughly go into into as a multiple the see how much you have to shift. Then see if it works by checking it.
e.g 140, 104, 56, 164, 80
take away 8 from each and they're all in the 12 times table. so... 12n+8