The correct choice is (a) 57 mm

For explanation I would say: Refer the figure below and the following steps-

• Draw the XY line. Draw two line perpendicular to XY line separated by a horizontal DISTANCE of 40 mm.

• Along the first line mark points a’ and a 24 mm above and 10 mm below XY line.

• Along the second line mark b and b’ 46 mm above and below XY line.

• Draw a reference line X1 Y1 parallel to line ab to represent the AVP.

• Through a and b, draw projectors to X1 Y1 line and extend it.

• Mark a2’ such that 3-a2’ = 5-a’. SIMILARLY mark B2’ such that 4-b2’ = 6b’.

• Join a2’-b2’ to obtain the TRUE length of the line.

• The inclination of the line a2’-b2’ with X1Y1 line is the true inclination of the line with HP.

• Draw X2Y2 parallel to the front VIEW a’b’ and project the auxiliary top view a1b1 in the similar manner.The inclination of the line a1-b1 with X2Y2 line is the true inclination of the line with VP.

By measurement, the following dimensions are obtained:

True length of the line is 57 mm.