\begin{Schunk}
\begin{Sinput}
 ps80 <- testSlopes(ps70)
\end{Sinput}
\begin{Soutput}
Values of x2 OUTSIDE this interval:
         lo          hi 
-0.02071143  0.85376194 
cause the slope of (b1 + b2*x2)x1 to be statistically significant
\end{Soutput}
\begin{Sinput}
 plot(ps80)
\end{Sinput}
\end{Schunk}
