this is a link to a web sight with a diagram to help you
https://www.google.com/url?sa=i&source=images&cd=&ved=2ahUKEwjw4v7knNDgAhVyUN8KHWgWD-wQjRx6BAgBEAU&url=%2Furl%3Fsa%3Di%26source%3Dimages%26cd%3D%26ved%3D%26url%3Dhttps%253A%252F%252Ffuturism.com%252Fwhere-do-all-the-elements-come-from%26psig%3DAOvVaw19_FOCuWs_nMsyY1YT0Da-%26ust%3D1550955269844922&psig=AOvVaw19_FOCuWs_nMsyY1YT0Da-&ust=1550955269844922
I Think The answer is d I hope it helps My friend Message Me if I’m wrong and I’ll change My answer and fix it for you
Answer:
649.8420 nm
Explanation:
We have given 
we have to find unknown wavelength that is 
The condition for constructive interference is 
Where d is distance between slits
is angle of emergence and n is order of maxima
Using constructive interference equation
---------eqn 1
---------eqn 2
On dividing eqn 1 by eqn 2


they are heated to extremely high temperatures. they are cooled to extremely low temperatures. they are made to be very thick.