Question 1009451
{{{D=Rt}}}
.
.
{{{D[1]=3.5R*t}}}
{{{D[2]=R*t}}}
.
.
When {{{t=6}}}
{{{D[1]-D[2]=1620}}}
Substituting,
{{{3.5R(6)-R(6)=1620}}}
{{{21R-6R=1620}}}
{{{15R=1620}}}
{{{R=108}}}{{{mph}}}<--- Average speed of second plane
{{{3.5R=378}}}{{{mph}}} <--- Average speed of first plane