We know M1D1T1/W1 =M2D2T2/W2 [Here W1 and W2 is the quantitative value of making chairs;W1 is 460 given]
Thus 12 x 24 x 6 / 460 = 18 x 36 x 8 / W2 [T1 & T2 are the quantitative values of time invested/day in making the chairs]
=> W2= 1380 (OPTION D)