y = 2x - 0.1x2
dy/dx = 2 - 0.2x
d2y/dx2 = -0.2
Since, d2y/dx2 < 0 , maximum value of y can be obtained by solving the equation dy/dx = 2 - 0.2x = 0
2 - 0.2x = 0
2 = 0.2x
Hence, x = 2/0.2 = 10
y = 2x - 0.1x2 = 2(10) - 0.1(10)2 = 20 - 0.1(100) = 20 - 10 = 10
Thus, Answer is B) 10 metres :)