In the context of backups, what is a retention

Select the option in which the numbers are related in the same way as are the number of the following set.

(4, 8, 40)

Select the number from among the given options that can replace the question mark (?) in the following series.

4, 21, 85, 256, 513, ?

Which two numbers from amongst the given options should be interchanged to make the given equation correct?

(240 ÷ 2 + 5) × 8 + 15 × 8 = 100

If ACE = 135 and ACER = 13518, then ACCURATE =

Select the combination of letters that when sequentially placed in the blanks of the given letter series will complete the series.

If 25 @ 20 = 5 and 28 @ 23 = 14, then 26 @ 21 = ?'. What will come in place of question mark?