Which one set of letters when sequentially placed at the gaps in the given letter series shall complete it.

d_ _td_s_d_st

A series is given, with one term missing. Choose the correct alternative from the given options that will complete the series.
51    (?)    57      65      81    

Find the next term in the given series.
B2, K12, T72, ______

Find out the missing numbers from the given alternatives.

Which of the following represents all such Government employees who are not Scientists?

_aa_ba_bb_ab_aab 

The ratio of the number of girls to the number of boys in a town is 90 %. If the total number of boys and girls in the town is 190, how many girls are in the town? 

Direction : Study the following information to answer the given questions:
A word and number arrangement machine when given an input line of words and numbers rearranges them following a particular rule. The following is an illustration of input and rearrangement.
Input : 52 peak 91 snow freeze 46 cold 15 high 31 73 trek
Step I : 15 52 peak snow freeze 46 cold high 31 73 trek 91
Step II: 15 31 52 peak snow freeze 46 cold high trek 73 91
Step III: 15 31 46 peak snow freeze cold high trek 52 73 91
Step IV: 15 31 46 cold peak snow freeze high trek 52 73 91
Step V : 15 31 46 cold peak freeze peak snow high trek 52 73 91
Step VI : 15 31 46 cold freeze high peak snow trek 52 73 91
Step VI is the last step of the rearrangement. As per the rules followed in the above steps, find out in each of the following questions the appropriate steps for the given input.
Input : 67 hot sun 19 best 83 ice 49 ace 77 cut 37
How many steps would be needed to complete the arrangement?