Question 149146
For Monday:
{{{d = r*t}}}
{{{d = 40t}}}
For Tuesday 
{{{280 - d = r*t}}}
{{{280 - d = 50*(t + 2)}}}
This is 2 equations with 2 unknowns
{{{280 - 40t = 50*(t + 2)}}}
{{{280 - 40t = 50t + 100}}}
{{{90t = 180}}}
{{{t = 2}}} hrs
She drove 2 hrs on Monday
check:
{{{d = 40t}}}
{{{d = 40*2}}}
{{{d = 80}}} mi
{{{280 - d = 50*(t + 2)}}}
{{{280 - d = 50*4}}}
{{{280 - d = 200}}}
{{{d = 80}}} mi
OK