Artificial methods in common use include preventing the sperm from reaching the ovum (using condoms, diaphragms, etc), inhibiting ovulation (using oral contraceptive pills), preventing implantation (using intrauterine devices), killing the sperm (using spermicides)
This can be solved by setting up a proportion.
The answer and steps are attached
333.75 mg would be a suitable dose for a 135 lb man.