One number Answer: A. -16
Step-by-step explanation: To get the value that should fit into the 1st place, we need to get the relationship between the numbers in the series(known as 'common difference' denoted by 'd'). This number is added to the previous value to get the next, and is gotten by subtracting the previous number from the preceding one. In this case,
d=(38-29)=9, (29-20)=9, (11-2)=9
So, the missing number is gotten by subtracting 9(since we're reversing the order) i.e -7-(9)= -7-9 = -16
Hope it helps!