In which state is the Hogenakkal Falls

What value should come in the place of (?) in the following number series?

15, 21, ?, 41.16, 57.624

168, 164, 155, 139, ?, 78

6, 30, 43, 58, 75, ?

What will come in place of the question mark (?) in the following series?

4000, ?, 320, 192, 153.6, 153.6

945, 1890, ?, 504, 144, 32

{(12√5 + 6√5 )} ×{(10√5 - 5√5 )} - 8² + 6² = ?

654, 647, 633, 612, 584, ?

120, 130, 145, 165, ?,  220

What will come in place of the question mark (?) in the following series?

45, 54, 72, ?, 126, 162