Energy in a magnetic field

[abot]

the problem reads... the magnetic field inside a superconducting solenoid is 4.50T. the solenoid has an inner diammeter of 6.20cm and length 26.0cm.
Determine (a) the magnetic energy density in the field. (b) he enrgy stored in the magnetic field with in the solenoid.

For (a) i use the formula Ub= (B^2)/(2Uo) and i get 8.1x10^6
Is this correct?

For (b) im not quite sure what to do. I know i must use the length and diameter to find B. or maybe not

I need some guidance.

Thank You

[Doc Al]

For (a) i use the formula Ub= (B^2)/(2Uo) and i get 8.1x10^6
Is this correct?
Yes. (Check your arithmetic.)

For (b) im not quite sure what to do. I know i must use the length and diameter to find B. or maybe not
Hint: The energy density that you found in (a) is the energy per unit volume.

[Gokul43201]

If you had written the units for your first part, the second part would become obvious. Never leave out the units; they are essential.