You want the equation for a line that goes through the data points (0, 248) and (5, 277). The slope is ∆y/∆x = (277-248)/(5-0) = 29/5 = 5.8. The first data point is the y-intercept, so your equation in slope-intercept form is
... y = 5.8x + 248 . . . . . . where y is MWh of generation and x is years since 2007.
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∆y is read "delta y". It means "the change in y".
