please see the image.....can anybody answer this.....

Since, F = qV X B
F contains i-component and k-component. So, go backwards and find B components and its directions using cross product’s RHTL (Thumb rule) by finding component that gives -i and k when cross producted with -j.
b) Yes. Since(j X j) = 0, so, j component of B can't be determined as the F doesn’t has the values corresponding to j component of B.
c) Simple dot product.