consider east-west direction along x-axis and north-south direction along Y-axis
A = displacement in north direction = 2 j
B = displacement in west direction = - 4 i
C = displacement in south direction = - 2 j
total distance travelled is given as
Distance = |A| + |B| + |C| = 2 + 4 + 2 = 8 blocks
displacement is given as
displacement = A + B + C
displacement = 2 j - 4 i - 2 j
displacement = - 4 i
hence the displacement is 4 blocks in west direction.
magnitude of displacement = 4 blocks
they've walked _8 blocks_____ blocks and have a total displacement (magnitude only) of four blocks