Question 227076
You need 2 equations: 1 for going to the beach, 
and one for returning
{{{d = r[1]*t[1]}}}
{{{d = r[2]*t[2]}}}
given:
{{{d = 36}}} km
{{{r[1] = 48}}} km/hr
{{{r[2] = 60}}} km/hr
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I can now rewrite the equations
{{{36 = 48*t[1]}}}
{{{36 = 60*t[2]}}}
This is 2 equations and 2 unknowns, so I can solve 
{{{t[1] = 36/48}}}
{{{t[1] = 3/4}}}
and
{{{t[2] = 36/60}}}
{{{t[2] = 3/5}}}
Note that
{{{3/4}}}hr x {{{60}}}min/hr = {{{45}}}min
and
{{{3/5}}}hr x {{{60}}}min/hr = {{{36}}}min
{{{t[1] + t[2] = 45 + 36}}} min
{{{45 + 36 = 81}}}min
and
{{{81 - 60 = 21}}}
He spent 1 hour and 21 min driving
check answer:
{{{36 = 48*t[1]}}}
{{{36 = 48*(3/4)}}}
{{{144 = 144}}}
and
{{{36 = 60*(3/5)}}}
{{{180 = 180}}}
OK