$($a$)$ How many fringes appear between the first diffraction$-$envelope minima to either side of the central maximum in a double$-$slit pattern if $=496nm,d=0\mathrm{.}193mm,$ and $a=34\mathrm{.}4m?($b$)$ What is the ratio of the intensity of the third bright fringe to the intensity of the central fringe?

$($a$)$ Number

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$($b$)$ Number $$ Units