help friend to ask you guys about:

nearly 10 year marriage,hu*****and(nearly 50years old) wants to divorce because the wife(nearly 45year sold) can not give birth a child,the hu*****and agree to pay alimony to his wife for her life time, his wife does not have a job.the annual income of the hu*****and is 87000, they live in CA. the question is: according to the law, how much the alimony should be monthly? or what is the percentage(as to the income)? thank you very much for sharing the infomation.