How much energy is stored in a 2.90-cm-diameter, 14.0-cm-long solenoid that has 200 turns of wire and carries a current of 0.790 ?

Answer 1

Compute the inductance L, in Henries.
The formula you need is here:
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indsol.html

The stored energy is
E = (1/2) L I^2

E will be in Joules if I is in amperes.