Question 1079804

Two mistakes.
Time is measured in minutes.
Rate is measured in miles/hour. 
You must convert one of them to be consistent.
{{{3(mile/hr)*(1/60)(hr/min)=(1/20)(mile/min)}}}
{{{4(mile/hr)*(1/60)(hr/min)=(1/15)(mile/min)}}}
{{{(1/20)(t+7)=(1/15)(t-5)}}}
{{{t=41}}}{{{min}}}
Answer is the same but the units are now correct.
When you measured distance, you have to use either of the formulas,
{{{d=(1/20)(t+7)}}}
{{{d=(1/15)(t-5)}}}
If you use {{{d=3t}}}, you'll get the wrong answer since {{{d=3t}}} and {{{d=4t}}} would give you different answers.
{{{d=(1/20)(48)=48/20=2.4}}}{{{miles}}}
{{{d=(1/15)(36)=2.4}}}{{{miles}}}