NMOS 2010 Q5

An(1 h) + Bo(1 h) --> 1/16.8


An (1 h) + Ch(1 h) --> 1/21


Bo(1 h) + Ch(1 h) --> 1/28



Bo(1 h) - Ch(1 h) --> 1/16.8 - 1/21 = 1/84

2 Bo(1 h) --> 1/84 + 1/28 = 1/21
Bo(1 h) --> 1/2 x 1/21 = 1/42

1/42 wall --> 1 h
1 wall --> 42 x 1 = 42 h ---- B

An(1 h) --> 1/16.8 - 1/42 = 1/28
1 wall --> 28 x 1 = 28 h ----- A

Ch(1 h) --> 1/28 - 1/42 = 1/84
1 wall --> 84 x 1 = 84 h ---- C

A + B + C = 28 + 42 + 84
                 = 154 h