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There is no formal limit (posts not topics), unless you get reported for spamming, in which case your account will be banned.
There is a cool down time though between posts:
waittime = 360;
if(activity >= 15)
waittime = (int)(90 - activity);
if(activity >= 60)
waittime=(int)(34.7586 - (0.0793103 * activity));
if(activity >= 100)
waittime = max((int)(14-(activity/50)), 4);
The cool down time therefore is relative to your activity. In your case, your activity is 42, so wait time should be 48 seconds (90-42) between posts.