Keeping the instrument height as 1 m, length of staff 4 m, the up gradient of the ground 1 in 10, the sight on the up slope must be less than

ANS:C - 45 m

Solution;

Note: Here in Q it is not 1 1/2 actually it is only 1/2 so,
if upward slope asked then i.e +ve.
Sight= (Staff ht + instrument ht.)/(Slope)
Sight=(4+1/2)(1/10)
Sight=(4.5)*(10)
Sight=45 m.

And It will be 55 m in case if 1 1/2 only. Slope = 1/10,
H.I = 1/2 = 0.5,
Sight = (0.5 + 4)/1 ÷ 10 = 45.