@Anonymous wrote:you can link your personal prime to your business account
log in to your personal account
click Your Account > Prime > Share Your Prime Benefits
choose extend Prime shipping to your Amazon Business account
enter your login credentials and then click Extend your Prime shipping benefits
I tried i get this message
"Share your Prime benefits
Amazon Household
The Amazon Household Program enables two adult family members and up to four children to share the best of Prime. Both Household adults can manage parental controls with Amazon FreeTime for children in the Amazon Household. Create your Amazon Household and start sharing your Prime benefits today.
Manage my household" and only lets me add family members, not business account. Amazon rep told me I couldnt do it anymore and needed to add the additional Business Prime $179 per year 
In my experiences with Prime, the trick posted by @inverse only works if you are OFFERED A FREE TRIAL of Prime. The way I have done twice before (thrice, if you count my Christmas shenanigans from tonight. See attached), is whenever you see a "try Prime for free" link next to an item you're about to add to cart--just go ahead with the trial and proceed with @inverse's instructions from there. Also, make sure the stars in the heavens above are aligned such that you get offered the Prime trial while you're logged into your Amazon Business account.
Here's a proof that the trick works as of couple moments ago:
