The stall speed increases
as the square root of the weight change, not just in proportion. Thus a
doubling of weight increases the stall speed not by a factor of 2 but by 1.414.
In this case the difference is 135 ÷ 120 = 1.125 and the stall speed increases
by the square root of that, 1.061.
Question NOT USED
in UK exams