Jerry started doing sit-ups every day. On the first day, he did 18 sit-ups. Every day after that he did 4 more sit-ups than he had done the previous day. Today Jerry did 26 sit-ups. Enter an equation that could be solved to find the number of days Jerry has been doing sit-ups, not counting the first day.
The equation __ d + __= __can help find the number of days Jerry has been doing sit-ups.