The images $($A$,$ B & C$)$ below are all taken from a screen during a double slit experiment

$-$ Part $($a$)$

On figure A $($top$),$ what are all the locations on the screen where the path difference from the two slits to that point on the screen is an integer number of wavelengths? $($Don$\text{'}$t worry about the sign of the position, just the magnitude.$)$

$-$ Part $($b$)$

On figure B $($middle$),$ what are all the places on the screen where the path difference from the two slits to that point on the screen is a half$-$integer number of wavelengths?

$-$ Part $($c$)$

On figure C $($bottom$),$ what are all the places on the screen where there is an integer value of m $($in the formula $$r $=$ m$)?$