Question 721213
M(x) =19x-x^2
since the coefficient associated with the x^2 is NEGATIVE we know it is a parabola that opens downwards.  Therefore, the vertex is the maximum.
x-value of vertex:
x = -b/(2a)
x = -19/(2(-1))
x = -19/(-2)
x = 9.5 inches (answer)