Question 1029726
{{{R*t=D}}}
.
.
Trip to game,
1.{{{R*t=40}}}
.
.
Trip back from game,
2.{{{(R-20)*(t+1)=40}}}
From 1,
{{{R=40/t}}}
Substituting into 2,
{{{(40/t-20)(t+1)=40}}}
Multiply both sides by t,
{{{(40-20t)(t+1)=40t}}}
{{{40t+40-20t^2-20t=40t}}}
{{{-20t^2-60t+40=0}}}
{{{t^2+3t+2=0}}}
{{{(t+3)(t-1)=0}}}
Only positive time solutions make sense,
{{{t-1=0}}}
{{{t=1}}}
So then,
{{{R=40/1}}}
{{{R=40}}}
She drove at 40 mph.