Jerry started doing sit-ups every day. On the first day, he did 11 sit-ups. Every day after that he did 4 more sit-ups than he had done the previous day. Today Jerry did 49 sit-ups. Write an equation that could be solved to find the number of days Jerry has been doing sit-ups, not counting the first day. Let n represent the number of days.

An equation that can help Jerry to find the number of days he has been doing sit-ups is given by ___ + ___ = ___.