How long is the diagonal of the box whose length width and height are 30cm 24cmand 18cm respectively?

the equation is L^2= w^2 + h^2 + l^2 where L= length of diagonal, w=width, h=height, and l= length,

L= sqrt( (30)^2 + (24)^2 + (18)^2)= (approx) 42.2 cm