Using the formula $=$ xd$/$nL$,$ describe how the following changes affect the $$x$$ distance in an interference pattern. a$.$ decreasing the wavelength $(1$ mark$)$ b$.$ decreasing the $$d$$ distance $(1$ mark$)$ c$.$ increasing the length to the screen $(1$ mark$)$ d$.$ Describe how a diffraction grating produces a spectrum. $(2$ marks$)$