Mount St. Helens is an 'active stratovolcano' located

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

23, 46, ?, 184, 368, 736

If √n + (1/√n) = 6, then find the value of n + (1/n).

If 9 : 12 :: 12: x, and 28: 42:: 42: y, then the value of 2x + y is: 

In ∆ ABC, MN ‖ BC, the area of quadrilateral MBCN=130 sqcm. If AN : NC = 4 : 5, then the area of ∆ MAN is:

If = -2 then find

If a = 2 + √3, then the value of (a⁶ + a⁴ + a² + 1)/a³ is

If n = 6 + √13, then find the value of (n + 1/n)².