Question 1051201
{{{R[1]*t[1]+R[2]*t[2]=21}}}
{{{12t[1]+8t[2]=21}}}
and
{{{t[1]+t[2]=2}}}
{{{t[1]=2-t[2]}}}
Substituting,
{{{12(2-t[2])+8t[2]=21}}}
{{{24-12t[2]+8t[2]=21}}}
{{{-4t[2]=-3}}}
{{{t[2]=3/4}}}
and
{{{t[1]=2-3/4}}}
{{{t[1]=5/4}}}
45 minutes at 8 mph and 1 hr 15 min at 12 mph.