The velocity of heat radiation in a vacuum

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

64, 60, 52, 40, ?, 4

Four terms are in proportion. The first, second and fourth terms are 4, 22, and 33. Find the third term.

If 4     x       4           7          15        38.5

Then,  ( x  + 1) ( x  - 1) = ?

6 6 3 6.5 12 33

26 63 124 215 342 511 ?

140     300     380      420      440      ?

10      14       41       ?         182        218

66       187       43       212       ?       241