A graphing calculator can do a linear regression on these points very easily. The y-intercept is 107.
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If you want to do this by hand, you can use the 2-point form of the equation for a line, then evaluate for x=0.
.. y = (100 -102)/(35 -25)*(x -25) +102
.. y =-2/10*(0 -25) +102
.. y = 107
