Two 15cm long flat glass plates are separated by a T (10 micro m) thick spacer at one end, leaving a thin wage of air between them. The plates are illuminated by light from a sodium lamp with wavelength (lamda) 589 nm. Alternating dark and bright fringes are observed. Find a relation among spacing between adjacent fringes delta x, lamda, L, and T. Also find the numerical value of the spacing between two fringes.