Convert the problem into an algebraic one of simultaneous equations.
x = 4/11 of the total length and y = 7/11 of the total length
11x = 4z and 11y = 7z so y = 7(11x/4) / 11 = 7x/4
y= x + 9
7x/4 = x+9
7x = 4x +36
3x = 36 so x= 12
Therefore y = 12+9 = 21