Velocity and acceleration vectors of a charged particle moving in a magnetic field at some instant are $\vec{v}=3\hat{i}+4\hat{j}$ and $\vec{a}=2\hat{i}+x\hat{j}$. Select the correct alternative(s) :

A proton moving with a velocity of $(6\hat{i}+8\hat{j})\times 10^{5}m{s}^{-1}$ enters uniform magnetic field of induction $5\times 10^{-3}\hat{k}T$ . The magnitude of the force acting on the proton is :
($\hat{i},\hat{j}$ and $\hat{k}$ are unit vectors forming a right handed triad)