Which of the following numbers will replace the question mark (?) in the given series?
91, 102, 139, ?, 187, 198, 235

Let's look at the differences between successive numbers:
102−91=11

139−102=37

Let's check the end of the series:

198−187=11

235−198=37

The difference pattern is clearly repeating: +11,+37,+11,+37,…
Applying this pattern to find the missing term:
?=139+11=150

Let's verify if adding 37 to 150 yields the next number:
150+37=187
This perfectly matches. So the missing number is 150.