Answer:
The magnetic field is
T
Explanation:
Given:
Velocity of electron 
Electric field 
The force on electron in magnetic field is given by,
......(1)
The force on electron in electric field is given by,
......(2)
Compare both equation,

Here 



T
Therefore, the magnetic field is
T
-- Since it's a cube, its length, width, and height are all the same 4 cm .
-- Its volume is (length x width x height) = 64 cm³ .
-- Density = (mass) / (volume)
= (176 g) / (64 cm³)
= 2.75 gm/cm³ .
Please find attached photograph for your answer. Hope it helps. Please do comment