A diffraction grating has $6900$ lines$/$cm$.$ What is the slit separation?

a$.$

$6\mathrm{.}9$E$3$m

b$.$

$1\mathrm{.}4$E$6$m

c$.$

$1\mathrm{.}4$E$9$m

d$.$

$6\mathrm{.}9$E$7$m

e$.$

Not$$enough$$information