Answer
$(a) \phi_1>\phi_2>\phi_3$
flux in face 1 > flux in face 3 > flux in face 2
Work Step by Step
$flux = magnetic field \times area \times cos(\theta)$
let the magnitude of magnetic field be B and area be A
flux at surface $1 = B \times A \times cos(20)$
flux at surface $1 = 0.9396BA$
flux at surface $2 = B times A \times cos(90)$
flux at surface $2 = 0$
flux at surface $3 = B \times A \times cos(70)$
flux at surface $3 = 0.342 \times BA$
so the ranking of the flux is
flux in face 1 > flux in face 3 > flux in face 2
