Every Observation Entered Twice

An analyst builds a dataset of 100 observations and regresses $y$ on a single predictor plus an intercept. By mistake she appends a second, identical copy of the file before running it, so the regression sees 200 rows: every original row appearing exactly twice. Compared with the correct regression, what happens to (a) the estimated coefficients, (b) the $R^2$, and (c) the reported $t$-statistics?