The magnetic force on a moving charged particle is given by F=q(v×B).
Since the acceleration a is in the direction of the magnetic force, it must be perpendicular to the magnetic field B.
Therefore, the dot product of acceleration and magnetic field is zero:
a⋅B=0
Substituting the given vectors:
(4i^−2xj^)⋅(3i^+2j^)=0
(4)(3)+(−2x)(2)=0
12−x=0
x=12
Answer: 12