Measuring the actual impact of experiment launches

As a pretty new data scientist in big tech I churn out a lot of experiment launches but haven't had a stakeholder ask for this before.

If we have 3 experiments that each improved a metric by 10% during the experiment, we launch all 3 a month later, and the metric improves by 15%, how do we know the contribution from each launch?

big churn data datascience data scientist experiment impact launch measuring new data scientist stakeholder tech