I'm measuring the garbage output of various cities in my country. I have 5 independent variables as predictors measured at 4 time points.

I'm not interested in the effects of time. I just want to know the regression coefficients for each of my variables. To find that out, I could do 4 separate multiple regressions, one for each time point. But that wouldn't summarize the data well, since I would have 4 sets of results. So my question is, is there a way to enter the data for all four time points and get one set of regression coefficients?