Physics Young's Double Slit Problem

In a Young’s Double Slit experiment, the separation of four bright fringes is $2.5 mm$, the wavelength of light used is $6.2 cdot 10^{-7} m$. If the distance from the slits to the screen is $80 cm$, calculate the separation of two slits.

I applied $frac{4lambda D}{d}=1.5cdot 10^{-3} m$
but the answer didn’t match. It matches when I use $frac{3lambda D}{d}$ instead of $4$.

Shouldn’t the separation of four bright fringes be $frac{4lambda D}{d}$ (after applying $sintheta = tantheta$ approximation)?

$D$ :distance from the slits to the screen

$lambda$: wavelength of light used

$d$: separation of the slits