How long and how often should get a sun exposure to get vitamin d? i work in an office & don't get much sun.is it true i should have calcium together?

It varies: This depends on your latitude, time of year, your skin pigmentation & how much skin is exposed. It D helps us absorb calcium but many get enough calcium via diet. It's more important to take Vit K. If you don't get enough sun take 5-8000 iu of Vit D/day. See http://www.vitamindcouncil.org/about-vitamin-d/how-do-i-get-the-vitamin-d-my-body-needs/ It's wise to test your Vit D levels; 50-80 is ideal.