Answer: they are adding 30 each time
Explanation:
in 320 to 350, it adds 30 because 20 plus 30 equals 50 then you can add 300 which is 350 then 350 plus 30 is 380 which is also the next number which means you are adding 30 each time and for the first box you subtract 30 from 350 which is 320 and for the last box you add 30 which is 380 + 30 which is 410 so that is your answer.