Let the temperature today be x °F.
Change in temperature after 1 day = [tex](x - \frac{7}{18} )[/tex] °F
Change in temperature after 2 days = [tex](x - \frac{7}{18} ) - \frac{7}{18} = (x - 2*\frac{7}{18} )[/tex] °F
Change in temperature after 3 days
= [tex](x - 2*\frac{7}{18} ) - \frac{7}{18} = (x - 3*\frac{7}{18} )=(x - \frac{7}{6} )[/tex]°F
